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Radicals and roots — ACT practice questions

Practice 36 Radicals and roots questions in the app

What this topic is

Radicals and roots on the ACT Mathematics test covers products of square roots, conjugate pairs, and binomials that mix integers with roots.

A student has to multiply radicals, apply the difference of squares to a conjugate, expand a squared two-term radical expression, and then simplify until the result is an integer or a fully reduced radical. Items are usually a compact expression set equal to a question mark, with five answer choices that mix integers and leftover roots.

Common traps include dropping the middle term when squaring, keeping an unsimplified radical, or flipping a sign on a conjugate.

Sample questions

Pick an answer to see whether it is right — nothing is saved, and nothing needs an account.

Question 1Easier

5018=\sqrt{50}\cdot\sqrt{18}={} ?

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Answer: C — 30

50=52\sqrt{50}=5\sqrt{2} and 18=32\sqrt{18}=3\sqrt{2}, so the product is 152=3015\cdot2=30.

Question 2Easier

(7+2)(72)=(\sqrt{7}+\sqrt{2})(\sqrt{7}-\sqrt{2})={} ?

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Answer: C — 5

The factors are conjugates, so their product is the difference of squares: (7)2(2)2=72=5(\sqrt{7})^2-(\sqrt{2})^2=7-2=5.

Question 3Mid

(232)2=(2\sqrt{3}-\sqrt{2})^2={} ?

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Answer: A — 144614-4\sqrt{6}

Using (ab)2=a22ab+b2(a-b)^2=a^2-2ab+b^2 gives x=1246+2=1446x=12-4\sqrt{6}+2=14-4\sqrt{6}.

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Practice 36 Radicals and roots questions in the app

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