Trapezoids

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SAT Math › Trapezoids

Questions 1 - 8
1

Square 1

The above figure shows Square . is the midpoint of ; is the midpoint of ; is the midpoint of . Construct .

. Which of the following expresses the length of in terms of ?

Explanation

Construct as shown in the diagram below:

Square 1

Quadrilateral is a rectangle, so opposite sides are congruent. Therefore, .

Since is the midpoint of ,

Since is the midpoint of ,

.

is a right triangle, so, by the Pythagorean Theorem,

Substituting:

Apply the Product of Radicals and Quotient of Radicals Rules:

2

Square 1

The above figure shows Square . is the midpoint of ; is the midpoint of ; is the midpoint of . Construct .

. Which of the following expresses the length of in terms of ?

Explanation

Construct as shown in the diagram below:

Square 1

Quadrilateral is a rectangle, so opposite sides are congruent. Therefore, .

Since is the midpoint of ,

Since is the midpoint of ,

.

is a right triangle, so, by the Pythagorean Theorem,

Substituting:

Apply the Product of Radicals and Quotient of Radicals Rules:

3

A trapezoid has a base of length 4, another base of length s, and a height of length s. A square has sides of length s. What is the value of s such that the area of the trapezoid and the area of the square are equal?

Explanation

In general, the formula for the area of a trapezoid is (1/2)(a + b)(h), where a and b are the lengths of the bases, and h is the length of the height. Thus, we can write the area for the trapezoid given in the problem as follows:

area of trapezoid = (1/2)(4 + s)(s)

Similarly, the area of a square with sides of length a is given by _a_2. Thus, the area of the square given in the problem is _s_2.

We now can set the area of the trapezoid equal to the area of the square and solve for s.

(1/2)(4 + s)(s) = _s_2

Multiply both sides by 2 to eliminate the 1/2.

(4 + s)(s) = 2_s_2

Distribute the s on the left.

4_s_ + _s_2 = 2_s_2

Subtract _s_2 from both sides.

4_s_ = _s_2

Because s must be a positive number, we can divide both sides by s.

4 = s

This means the value of s must be 4.

The answer is 4.

4

A trapezoid has a base of length 4, another base of length s, and a height of length s. A square has sides of length s. What is the value of s such that the area of the trapezoid and the area of the square are equal?

Explanation

In general, the formula for the area of a trapezoid is (1/2)(a + b)(h), where a and b are the lengths of the bases, and h is the length of the height. Thus, we can write the area for the trapezoid given in the problem as follows:

area of trapezoid = (1/2)(4 + s)(s)

Similarly, the area of a square with sides of length a is given by _a_2. Thus, the area of the square given in the problem is _s_2.

We now can set the area of the trapezoid equal to the area of the square and solve for s.

(1/2)(4 + s)(s) = _s_2

Multiply both sides by 2 to eliminate the 1/2.

(4 + s)(s) = 2_s_2

Distribute the s on the left.

4_s_ + _s_2 = 2_s_2

Subtract _s_2 from both sides.

4_s_ = _s_2

Because s must be a positive number, we can divide both sides by s.

4 = s

This means the value of s must be 4.

The answer is 4.

5

Square 1

The above figure shows Square . is the midpoint of ; is the midpoint of ; is the midpoint of . Construct .

If Square has area , what is the area of Quadrilateral ?

Explanation

Let be the common sidelength of the square. The area of the square is .

Construct segment . This divides the square into Rectangle and a right triangle. The dimensions of Rectangle are

and

.

The area of Rectangle s the product of these dimensions:

The lengths of the legs of Right are

and

The area of this right triangle is half the product of these lengths, or

This is seen below:

Square 2

The sum of these areas is the area of Quadrilateral

.

Substituting for , the area is .

6

Square 1

The above figure shows Square . is the midpoint of ; is the midpoint of ; is the midpoint of . Construct .

If Square has area , what is the area of Quadrilateral ?

Explanation

Let be the common sidelength of the square. The area of the square is .

Construct segment . This divides the square into Rectangle and a right triangle. The dimensions of Rectangle are

and

.

The area of Rectangle s the product of these dimensions:

The lengths of the legs of Right are

and

The area of this right triangle is half the product of these lengths, or

This is seen below:

Square 2

The sum of these areas is the area of Quadrilateral

.

Substituting for , the area is .

7

Find the area of a trapezoid given bases of length 1 and 2 and height of 2.

Explanation

To solve, simply use the formula for the area of a trapezoid. Thus,

8

Find the area of a trapezoid given bases of length 1 and 2 and height of 2.

Explanation

To solve, simply use the formula for the area of a trapezoid. Thus,

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