Describe Cross-Sections of 3D Figures
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7th Grade Math › Describe Cross-Sections of 3D Figures
A rectangular pyramid is sliced by a vertical plane that passes through the apex (top point) and the center of the base. What 2D shape is the cross-section?
Parallelogram
Circle
Triangle
Rectangle
Explanation
This question tests describing 2D cross-sections from slicing 3D figures: horizontal slices of prisms/pyramids (rectangles), vertical slices through apex (triangles), horizontal slices of cylinders/cones (circles), based on slice orientation. Cross-section shape depends on slice orientation and 3D figure: rectangular pyramid sliced horizontally gives smaller rectangle (parallel to base, similar shape decreasing toward apex), sliced vertically through apex gives triangle (apex is vertex, base edge is side, isosceles if through center). For example, a rectangular pyramid sliced vertically through the apex shows a triangle cross-section (three vertices: apex and two base corners). The correct cross-section identification is a triangle, as the plane passes through the apex point and cuts the base edge, forming three sides. A common error is claiming it's a rectangle (wrong, triangle—vertical through apex creates a pointed shape, not rectangular). To determine the cross-section: (1) identify the 3D figure (rectangular pyramid), (2) identify slice orientation (vertical through apex), (3) apply rules (through apex→triangle), (4) name 2D shape (triangle). Key patterns: pyramid horizontal rectangle but vertical triangle (apex creates point), and orientation matters—horizontal vs vertical differ significantly.
A cylinder is sliced by a vertical plane that passes through the center axis of the cylinder. What 2D shape is the cross-section?
Ellipse
Circle
Pentagon
Rectangle
Explanation
This question tests describing 2D cross-sections from slicing 3D figures: horizontal slices of prisms/pyramids (rectangles), vertical slices through apex (triangles), horizontal slices of cylinders/cones (circles), based on slice orientation. Cross-section shape depends on slice orientation and 3D figure: cylinder horizontal gives circle (parallel to circular base maintains circular shape), vertical through axis gives rectangle. For example, a cylinder sliced vertically through the axis shows a rectangle cross-section (height as sides, diameter as width). The correct cross-section identification is a rectangle, as the plane cuts along the height and through the curved surface, unfolding to straight lines. A common error is claiming it's a circle (wrong, rectangle—vertical through axis, circle for horizontal). To determine the cross-section: (1) identify the 3D figure (cylinder), (2) identify slice orientation (vertical through axis), (3) apply rules (vertical through axis→rectangle), (4) name 2D shape (rectangle). Key patterns: cylinder horizontal circle but vertical rectangle, and common mistakes include confusing with ellipses (which occur for slanted slices).
A cylinder (like a soup can) is sliced by a horizontal plane parallel to its circular base. What 2D shape is the cross-section?
Triangle
Circle
Trapezoid
Rectangle
Explanation
This question tests describing 2D cross-sections from slicing 3D figures: horizontal slices of prisms/pyramids (rectangles), vertical slices through apex (triangles), horizontal slices of cylinders/cones (circles), based on slice orientation. Cross-section shape depends on slice orientation and 3D figure: cylinder horizontal gives circle (parallel to circular base maintains circular shape), vertical through axis gives rectangle. For example, a cylinder sliced horizontally shows a circular cross-section (parallel to the circular base, maintaining the round shape). The correct cross-section is a circle, as the horizontal slice parallel to the base of a cylinder follows the base's shape. A common error is choosing rectangle (wrong, as that's for vertical slices through the axis; horizontal in cylinders yields circles, not rectangles). To determine the cross-section: (1) identify the 3D figure as a cylinder, (2) note the slice is horizontal and parallel to the base, (3) apply the rule that parallel to the base gives the same shape as the base (circle), (4) name the 2D shape as circle. Key patterns include cylinders and cones producing circles for horizontal slices due to their circular bases, unlike prisms with rectangular ones, with mistakes confusing orientation and claiming rectangles from horizontal cuts.
A cereal box is shaped like a rectangular prism. You slice it with a horizontal plane parallel to the base. What 2D shape is the cross-section?
Rectangle
Triangle
Circle
Trapezoid
Explanation
This question tests describing 2D cross-sections from slicing 3D figures: horizontal slices of prisms/pyramids (rectangles), vertical slices through apex (triangles), horizontal slices of cylinders/cones (circles), based on slice orientation. Cross-section shape depends on slice orientation and 3D figure: rectangular prism sliced horizontally (parallel to base) gives rectangle cross-section (cuts through vertical faces creating rectangular outline), sliced vertically gives rectangle (through opposite faces). For example, a rectangular prism like a cereal box sliced horizontally parallel to the base shows a rectangle cross-section (top and bottom edges parallel, sides straight—rectangular outline). The correct cross-section identification is a rectangle, as the horizontal slice parallel to the base mirrors the rectangular base shape. A common error is thinking a horizontal prism slice gives a triangle (wrong, it's a rectangle—prism faces are rectangles, horizontal cuts parallel giving rectangle). To determine the cross-section: (1) identify the 3D figure (rectangular prism), (2) identify slice orientation (horizontal=parallel to base), (3) apply rules (parallel to base→same shape as base for prism), (4) name 2D shape (rectangle). Key patterns: prism horizontal/vertical both rectangles (rectangular faces), and orientation matters—horizontal vs vertical can differ in other shapes like pyramids.
Which slice would produce a triangle as the cross-section?
Choose the best option.
A horizontal slice parallel to the base of a cylinder
A horizontal slice parallel to the base of a rectangular prism
A horizontal slice parallel to the base of a cone
A vertical slice through the apex of a rectangular pyramid
Explanation
Tests describing 2D cross-sections from slicing 3D figures: horizontal slices of prisms/pyramids (rectangles), vertical slices through apex (triangles), horizontal slices of cylinders/cones (circles), based on slice orientation. Cross-section shape depends on slice orientation and 3D figure: rectangular prism sliced horizontally (parallel to base) gives rectangle cross-section (cuts through vertical faces creating rectangular outline), sliced vertically gives rectangle (through opposite faces). Rectangular pyramid sliced horizontally gives smaller rectangle (parallel to base, similar shape decreasing toward apex), sliced vertically through apex gives triangle (apex is vertex, base edge is side, isosceles if through center). For example, rectangular pyramid vertical through apex showing triangle (three vertices: apex and two base corners), or rectangular prism sliced horizontally showing rectangle cross-section (top and bottom edges parallel, sides straight—rectangular outline), or cylinder horizontal showing circular cross-section (parallel to circular base). The correct identification for producing a triangle is a vertical slice through the apex of a rectangular pyramid, as it cuts from the point to the base, forming three sides. A common error is choosing horizontal slice of a prism (wrong, rectangle—not tapering to point), or horizontal cone (wrong, circle—parallel to base). Determining cross-section: (1) identify 3D figure (prism, pyramid, cylinder, cone), (2) identify slice orientation (horizontal=parallel to base, vertical=perpendicular to base, through specific features like apex/axis), (3) apply rules (parallel to base→same shape as base for prism, smaller for pyramid/cone; through apex→triangle; vertical through cylinder axis→rectangle), (4) name 2D shape (rectangle, triangle, circle, etc.). Key patterns: prism horizontal/vertical both rectangles (rectangular faces), pyramid horizontal rectangle but vertical triangle (apex creates point), cylinder/cone horizontal circles (circular bases), vertical through axis rectangles or triangles (cone apex).
Which slice would produce a triangle as the cross-section?
Choose the best option.
A vertical slice through the apex of a rectangular pyramid
A horizontal slice parallel to the base of a rectangular prism
A horizontal slice parallel to the base of a cone
A horizontal slice parallel to the base of a cylinder
Explanation
Tests describing 2D cross-sections from slicing 3D figures: horizontal slices of prisms/pyramids (rectangles), vertical slices through apex (triangles), horizontal slices of cylinders/cones (circles), based on slice orientation. Cross-section shape depends on slice orientation and 3D figure: rectangular prism sliced horizontally (parallel to base) gives rectangle cross-section (cuts through vertical faces creating rectangular outline), sliced vertically gives rectangle (through opposite faces). Rectangular pyramid sliced horizontally gives smaller rectangle (parallel to base, similar shape decreasing toward apex), sliced vertically through apex gives triangle (apex is vertex, base edge is side, isosceles if through center). For example, rectangular pyramid vertical through apex showing triangle (three vertices: apex and two base corners), or rectangular prism sliced horizontally showing rectangle cross-section (top and bottom edges parallel, sides straight—rectangular outline), or cylinder horizontal showing circular cross-section (parallel to circular base). The correct identification for producing a triangle is a vertical slice through the apex of a rectangular pyramid, as it cuts from the point to the base, forming three sides. A common error is choosing horizontal slice of a prism (wrong, rectangle—not tapering to point), or horizontal cone (wrong, circle—parallel to base). Determining cross-section: (1) identify 3D figure (prism, pyramid, cylinder, cone), (2) identify slice orientation (horizontal=parallel to base, vertical=perpendicular to base, through specific features like apex/axis), (3) apply rules (parallel to base→same shape as base for prism, smaller for pyramid/cone; through apex→triangle; vertical through cylinder axis→rectangle), (4) name 2D shape (rectangle, triangle, circle, etc.). Key patterns: prism horizontal/vertical both rectangles (rectangular faces), pyramid horizontal rectangle but vertical triangle (apex creates point), cylinder/cone horizontal circles (circular bases), vertical through axis rectangles or triangles (cone apex).
A cone (like an ice cream cone) is sliced by a horizontal plane parallel to its circular base. What 2D shape is the cross-section?
Triangle
Square
Circle
Rectangle
Explanation
This question tests describing 2D cross-sections from slicing 3D figures: horizontal slices of prisms/pyramids (rectangles), vertical slices through apex (triangles), horizontal slices of cylinders/cones (circles), based on slice orientation. Cross-section shape depends on slice orientation and 3D figure: cone horizontal gives circle (smaller toward apex), vertical through apex gives isosceles triangle. For example, a cone sliced horizontally shows a circular cross-section (parallel to the base but smaller due to tapering). The correct cross-section is a circle, as the horizontal slice parallel to the base of a cone follows the base's round shape, just reduced. A common error is choosing triangle (wrong, as that's for vertical slices through the apex; horizontal in cones yields circles, not triangles). To determine the cross-section: (1) identify the 3D figure as a cone, (2) note the slice is horizontal and parallel to the base, (3) apply the rule that parallel to the base gives a smaller circle, (4) name the 2D shape as circle. Key patterns include cones producing smaller circles for horizontal slices due to tapering, similar to pyramids but with round bases, with mistakes confusing cones with prisms and claiming rectangles.
A cone (like an ice cream cone) is sliced by a vertical plane that passes through the apex and the center of the circular base. What 2D shape is the cross-section?
Rectangle
Triangle
Circle
Square
Explanation
Tests describing 2D cross-sections from slicing 3D figures: horizontal slices of prisms/pyramids (rectangles), vertical slices through apex (triangles), horizontal slices of cylinders/cones (circles), based on slice orientation. Cross-section shape depends on slice orientation and 3D figure: rectangular prism sliced horizontally (parallel to base) gives rectangle cross-section (cuts through vertical faces creating rectangular outline), sliced vertically gives rectangle (through opposite faces). Cone horizontal gives circle (smaller toward apex), vertical through apex gives isosceles triangle. For example, cone vertical through apex showing triangle (apex point and base diameter forming isosceles sides), or cone horizontal showing circular cross-section (parallel to base but smaller), or rectangular pyramid vertical through apex showing triangle (three vertices: apex and two base corners). The correct cross-section identification for a cone sliced vertically through the apex and base center is a triangle, as the plane cuts from the point to the base edges, creating three sides. A common error is thinking it's a circle (wrong, triangle—through apex forms point and straight lines), or a rectangle (wrong, tapers to point). Determining cross-section: (1) identify 3D figure (prism, pyramid, cylinder, cone), (2) identify slice orientation (horizontal=parallel to base, vertical=perpendicular to base, through specific features like apex/axis), (3) apply rules (parallel to base→same shape as base for prism, smaller for pyramid/cone; through apex→triangle; vertical through cylinder axis→rectangle), (4) name 2D shape (rectangle, triangle, circle, etc.). Key patterns: prism horizontal/vertical both rectangles (rectangular faces), pyramid horizontal rectangle but vertical triangle (apex creates point), cylinder/cone horizontal circles (circular bases), vertical through axis rectangles or triangles (cone apex).
A cone is sliced by a vertical plane that passes through the apex (the tip) and the center of the base. What 2D shape is the cross-section?
Rectangle
Circle
Trapezoid
Triangle
Explanation
This question tests describing 2D cross-sections from slicing 3D figures: horizontal slices of prisms/pyramids (rectangles), vertical slices through apex (triangles), horizontal slices of cylinders/cones (circles), based on slice orientation. Cross-section shape depends on slice orientation and 3D figure: cone horizontal gives circle (smaller toward apex), vertical through apex gives isosceles triangle. For example, a cone sliced vertically through the apex shows a triangle cross-section (apex as vertex, base diameter as base side). The correct cross-section identification is a triangle, as the plane passes through the tip and cuts the base, forming three sides. A common error is claiming it's a circle (wrong, triangle—vertical through apex, circle for horizontal). To determine the cross-section: (1) identify the 3D figure (cone), (2) identify slice orientation (vertical through apex), (3) apply rules (through apex→triangle), (4) name 2D shape (triangle). Key patterns: cone horizontal circle but vertical triangle (apex creates point), and orientation matters—horizontal vs vertical differ like in pyramids.
A soup can is shaped like a cylinder. You slice it with a horizontal plane parallel to the circular base. What 2D shape is the cross-section?
Trapezoid
Circle
Triangle
Rectangle
Explanation
This question tests describing 2D cross-sections from slicing 3D figures: horizontal slices of prisms/pyramids (rectangles), vertical slices through apex (triangles), horizontal slices of cylinders/cones (circles), based on slice orientation. Cross-section shape depends on slice orientation and 3D figure: cylinder horizontal gives circle (parallel to circular base maintains circular shape), vertical through axis gives rectangle. For example, a cylinder like a soup can sliced horizontally parallel to the base shows a circular cross-section (matching the base shape). The correct cross-section identification is a circle, as the horizontal slice parallel to the circular base preserves the round outline. A common error is thinking it's a rectangle (wrong, circle—parallel to circular base, rectangle for vertical slices). To determine the cross-section: (1) identify the 3D figure (cylinder), (2) identify slice orientation (horizontal=parallel to base), (3) apply rules (parallel to base→circle for cylinder), (4) name 2D shape (circle). Key patterns: cylinder/cone horizontal circles (circular bases), but vertical through axis rectangles or triangles (cone apex).