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Mathematics

Key features and transformations of graphs — ACT practice questions

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What this topic is

Shifts, stretches and reflections make up the transformation half of Key features and transformations of graphs.

Replacing x with x plus three moves a graph three units left, not right, which is the most frequent mix-up. Multiplying the whole function by a number stretches it vertically. A horizontal shift also carries a domain boundary along: if f is defined for x at least zero, then f of x plus three is defined for x at least negative three.

Among the key features are intercepts, slope, maximum and minimum points and asymptotes; ACT Mathematics asks for an intercept, a stretch factor or a shifted domain.

Sample questions

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Question 1Mid

The domain of f is all real x such that x≥−2. Let g(x)=f(x+6). Which of the following inequalities describes the domain of g?

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Answer: D — x≥−8

The input to f must satisfy x+6≥−2. Subtracting 6 gives x≥−8, which is the domain of g.

Question 2Easier

The graph of y=g(x) is a vertical stretch of the graph of y=f(x), where g(x)=af(x) and a>0. If f(4)=6 and g(4)=15, what is the value of a?

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Answer: B — 2.5

Since g(4)=af(4), the given values yield 15=6a. Thus, a=2.5.

Question 3Easier

In the standard (x,y) coordinate plane, a line has slope −2 and y-intercept 6. What is the x-intercept of this line?

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Answer: C — 3

The equation is y=−2x+6. Setting y=0 gives x=3. The number 6 is the y-intercept.

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