The equation above is true for all x, where a and b are constants. What is the value of ab ?
A
18
B
20
C
24
D
40
Correct answer: C
Explanation
Choice C is correct. If the equation is true for all x, then the expressions on both sides of the equation will be equivalent. Multiplying the polynomials on the left-hand side of the equation gives . On the right-hand side of the equation, the only -term is . Since the expressions on both sides of the equation are equivalent, it follows that , which can be rewritten as . Therefore, , which gives .
Choice A is incorrect. If , then the coefficient of on the left-hand side of the equation would be , which doesn’t equal the coefficient of , , on the right-hand side. Choice B is incorrect. If , then the coefficient of on the left-hand side of the equation would be , which doesn’t equal the coefficient of , , on the right-hand side. Choice D is incorrect. If , then the coefficient of on the left-hand side of the equation would be , which doesn’t equal the coefficient of , , on the right-hand side.
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id cb_question_bank:12b4e8a6-e7d5-4acc-9336-0f87f6f44eb1 · question 371cbf6b · IBN 11189-DC
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