Solving Nonlinear Functions

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SAT Math › Solving Nonlinear Functions

Questions 1 - 10
1

The function $p(x)=\dfrac{4}{x}+1$ is defined for real $x$ where possible. What is the range of $p(x)$?

$y\le 1$

$y\ne 1$

$y\ge 1$

$y\ne 0$

Explanation

We need to find the range of p(x) = 4/x + 1, a rational function. The term 4/x can take any value except 0 (since x ≠ 0 for the function to be defined). As x approaches 0 from the positive side, 4/x → +∞; as x approaches 0 from the negative side, 4/x → -∞; as x → ±∞, 4/x → 0. Therefore, 4/x can be any real number except 0, and p(x) = 4/x + 1 can be any real number except 1. The range is y ≠ 1. The horizontal asymptote at y = 1 confirms this. For rational functions of the form a/x + k, the range excludes y = k.

2

A coordinate plane shows a curve starting at $(4,0)$ and increasing to the right, passing through $(5,1)$ and $(8,2)$. Which equation best matches the graph?

$y=|x-4|$

$y=\dfrac{1}{x-4}$

$y=(x-4)^2$

$y=\sqrt{x-4}$

Explanation

We need to match an equation to a curve starting at (4,0) and passing through (5,1) and (8,2). This is a square root function since it starts at a point and increases at a decreasing rate. Testing y = √(x-4): at x = 4, y = √(4-4) = √0 = 0 ✓; at x = 5, y = √(5-4) = √1 = 1 ✓; at x = 8, y = √(8-4) = √4 = 2 ✓. The function starts at x = 4 because that's where the expression under the radical becomes zero. Square root functions have a starting point and increase gradually. The characteristic shape and the fact it starts at (4,0) rather than continuing left confirms this is a radical function.

3

A bacteria culture is modeled by $P(t)=120(1.35)^t$, where $t$ is the number of hours since the start. Which statement best describes the function and what it implies about the culture over time?

Exponential decay; multiplies by $0.65$

Linear; adds 35 each hour

Quadratic; increases by $t^2$

Exponential growth; multiplies by $1.35$

Explanation

This question asks us to identify the type of function P(t) = $120(1.35)^t$ and interpret what it means for the bacteria culture. The function has the form P(t) = $a·b^t$ where a = 120 and b = 1.35, which is the standard form of an exponential function. Since the base 1.35 > 1, this represents exponential growth where the population multiplies by 1.35 each hour. This means the population increases by 35% each hour (since 1.35 = 1 + 0.35). The key error would be confusing this with linear growth, which would add a constant amount each hour rather than multiply by a constant factor.

4

What is the domain of the real-valued function $g(x)=\sqrt{x-3}$?

$(-\infty,3]$

$(3,\infty)$

$(-\infty,\infty)$

$[3,\infty)$

Explanation

This question asks for the domain of g(x) = √(x-3), which is a square root function (radical function). For real-valued outputs, the expression under the square root must be non-negative: x - 3 ≥ 0. Solving this inequality: x ≥ 3. Therefore, the domain includes all values from 3 to infinity, including 3 itself, written as [3,∞). The square bracket at 3 indicates that x = 3 is included in the domain. A common error is using a parenthesis instead of a bracket, which would incorrectly exclude x = 3.

5

A coordinate plane shows an exponential curve that passes through $(0,8)$ and decreases to the right, passing near $(1,4)$ and $(2,2)$. Which equation best matches the graph?

$y=8-x$

$y=8\left(\dfrac12\right)^x$

$y=8(2)^x$

$y=4\left(\dfrac12\right)^x$

Explanation

We need to identify an exponential curve passing through (0,8), (1,4), and (2,2). This is exponential decay since values are decreasing. From 8 to 4 is ×1/2, and from 4 to 2 is also ×1/2, confirming constant ratio. Testing y = $8(1/2)^x$: at x = 0, y = $8(1/2)^0$ = 8(1) = 8 ✓; at x = 1, y = $8(1/2)^1$ = 8(1/2) = 4 ✓; at x = 2, y = $8(1/2)^2$ = 8(1/4) = 2 ✓. The decay factor of 1/2 means the function value halves with each unit increase in x. Exponential decay has base between 0 and 1. When consecutive y-values show constant ratios less than 1, it indicates exponential decay.

6

An object’s temperature difference from room temperature is modeled by $T(t)=18(0.75)^t$, where $t$ is in minutes. What is $T(2)$?

$10.125$

$13.5$

$9$

$6.75$

Explanation

We need to find T(2) for the exponential decay function T(t) = $18(0.75)^t$. This models temperature difference decreasing over time. Substituting t = 2: T(2) = $18(0.75)^2$ = 18(0.75)(0.75) = 18(0.5625) = 10.125. The calculation requires squaring 0.75: (0.75)² = 0.5625, then multiplying by 18. The decay factor 0.75 means 75% of the temperature difference remains each minute. Common errors include calculating 0.75² incorrectly or confusing it with 0.75×2. When evaluating exponential functions, carefully compute the power before multiplying by the coefficient.

7

A delivery drone’s distance from its starting point is modeled by $d(t)=|t-6|+2$, where $t$ is minutes after launch. What is $d(10)$?

$6$

$2$

$4$

$12$

Explanation

We need to find d(10) for the absolute value function d(t) = |t-6| + 2. This models a drone's distance, with the absolute value creating a V-shaped path. Substituting t = 10: d(10) = |10-6| + 2 = |4| + 2 = 4 + 2 = 6. The absolute value |10-6| = |4| = 4 represents the time difference from t = 6, and adding 2 gives the total distance. The vertex of this V-shaped function occurs at t = 6 where the distance is minimized at d(6) = |6-6| + 2 = 0 + 2 = 2. For absolute value functions, always evaluate the expression inside first, then take the absolute value.

8

For the function $f(x)=|2x-7|$, what is the value of $f(1)$?

$-9$

$-5$

$5$

$9$

Explanation

We need to find f(1) for the absolute value function f(x) = |2x - 7|. This is an absolute value function, which creates a V-shaped graph. To find f(1), substitute x = 1: f(1) = |2(1) - 7| = |2 - 7| = |-5| = 5. The absolute value operation takes the distance from zero, so |-5| = 5. A common error is forgetting to apply the absolute value and leaving the answer as -5. When working with absolute value functions, always remember the final step of taking the positive value.

9

A coordinate plane shows a curve that crosses the $y$-axis at $(0,2)$ and passes through $(1,6)$ and $(2,18)$. Which equation best represents the curve?

$y=2x+2$

$y=2\cdot 2^x$

$y=2\cdot 3^x$

$y=3x+2$

Explanation

We need to identify which equation matches a curve passing through (0,2), (1,6), and (2,18). This is clearly an exponential function since the y-values are multiplying by a constant factor: from 2 to 6 is ×3, and from 6 to 18 is also ×3. Testing y = $2·3^x$: at x = 0, y = $2·3^0$ = 2·1 = 2 ✓; at x = 1, y = $2·3^1$ = 2·3 = 6 ✓; at x = 2, y = $2·3^2$ = 2·9 = 18 ✓. The pattern of multiplying by 3 each time confirms exponential growth. Linear functions would add the same amount each time, not multiply. When data shows constant multiplication between successive y-values, it indicates an exponential function.

10

A coordinate plane shows a parabola opening upward with vertex at $(1,-4)$ and passing through $(0,-3)$. Which equation matches the graph?

$y=(x+1)^2-4$

$y=|x-1|-4$

$y=(x-1)^2-4$

$y=(x-1)^2+4$

Explanation

We need to match an equation to a parabola with vertex at (1,-4) passing through (0,-3). This is a quadratic function in vertex form: y = a(x-h)² + k where (h,k) = (1,-4). So y = a(x-1)² - 4. To find a, use the point (0,-3): -3 = a(0-1)² - 4; -3 = a(1) - 4; -3 = a - 4; a = 1. Therefore, y = (x-1)² - 4. We can verify: vertex is at (1,-4) ✓, and when x = 0: y = (0-1)² - 4 = 1 - 4 = -3 ✓. The parabola opens upward since a = 1 > 0. When given vertex and another point, use vertex form to find the equation.

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