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Quadratic equations — ACT practice questions

Practice 43 Quadratic equations questions in the app

What this topic is

Quadratic equations on the ACT Mathematics test cover finding zeros, rewriting equivalent forms, and using a known root to find a missing coefficient.

A student must expand vertex form, complete the square or factor, apply the quadratic formula, and use root-coefficient relationships. Items typically ask which choice gives both zeros, which equation is equivalent after rearranging, or the value of a parameter that makes a given solution work.

Common traps include listing only one zero, dropping a sign when moving terms, and treating a squared binomial as already solved. Answer choices usually list pairs of roots, rewritten equations, or one coefficient.

Sample questions

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Question 1Easier

Which of the following gives both zeros of f(x)=2(x3)218f(x)=2(x-3)^2-18?

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Answer: B — 0 and 6

Setting f(x)=0f(x)=0 gives 2((x3)29)=02\left((x-3)^2-9\right)=0, so 2x(x6)=02x(x-6)=0. Therefore the zeros are 0 and 6.

Question 2Easier

Which of the following is equivalent to x2+10x=11x^2+10x=11?

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Answer: A — (x+5)2=36(x+5)^2=36

Adding 25 to both sides gives x2+10x+25=36x^2+10x+25=36. The left side factors as (x+5)2(x+5)^2, so (x+5)2=36(x+5)^2=36.

Question 3Easier

One solution of the equation x2bx+18=0x^2-bx+18=0 is x=3x=3. What is the value of bb?

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Answer: C — 9

Substitute x=3x=3: 93b+18=027=3bb=99-3b+18=0\Rightarrow 27=3b\Rightarrow b=9.

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Practice 43 Quadratic equations questions in the app

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