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Mathematics

Polynomial expressions and factoring — ACT practice questions

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What this topic is

Recognizing patterns speeds up Polynomial expressions and factoring.

Squaring a binomial produces three terms, so x plus three, squared, equals x squared plus six x plus nine, not x squared plus nine, a mistake that drops the middle term. Factoring reverses multiplication, and grouping handles trinomials with a leading coefficient other than one. Some polynomials of degree four behave like quadratics in x squared, so substituting a new letter for x squared turns them into familiar problems.

ACT Mathematics asks which expression is equivalent to a given one or how many real zeros a polynomial has, and expanding a factored choice is a reliable way to confirm it.

Sample questions

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Question 1Easier

Which of the following expressions is equivalent to (2x+3)2?

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Answer: A — 4x2+12x+9

(2x+3)2=(2x)2+2(2x)(3)+32=4x2+12x+9.

Question 2Easier

Which of the following expressions is equivalent to 10t2−17t+6?

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Answer: A — (5t−6)(2t−1)

Expanding (5t−6)(2t−1) gives 10t2−5t−12t+6. Combining the middle terms yields 10t2−17t+6.

Question 3Mid

How many distinct real zeros does p(x)=x4−5x2+4 have?

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Answer: D — 4

Treat the expression as a quadratic in x2: x4−5x2+4=(x2−1)(x2−4). Thus, the distinct real zeros are −2,−1,1, and 2, for a total of 4.

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