Question which-

2.2 Nonlinear Equations in One Variable - Quadratic solving (factoring, quadratic formula, completing square)
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2 x squared, minus 2, equals 2 x plus 3

Which of the following is a solution to the equation above?

A.

2

B.

1 minus the square root of 11

C.

one half plus the square root of 11

D.

the fraction with numerator 1 plus the square root of 11, and denominator 2

Which of the following is a solution to the equation above?

Hard-difficulty · SAT Math · Nonlinear Equations in One Variable — Quadratic solving (factoring, quadratic formula, completing square). Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.

Answer explanation

Choice D is correct. A quadratic equation in the form a, x squared, plus b x, plus c, equals 0, where a, b, and c are constants, can be solved using the quadratic formula: x equals, the fraction with numerator negative b plus or minus the square root of b squared, minus 4 a c, end root, and denominator 2 a, end fraction. Subtracting 2 x plus 3 from both sides of the given equation yields 2 x squared, minus 2 x, minus 5, equals 0. Applying the quadratic formula, where a, equals 2, b equals negative 2, and c equals negative 5, yields x equals the fraction with numerator negative, open parenthesis, negative 2, close parenthesis, plus or minus the square root of, open parenthesis, negative 2, close parenthesis, squared, minus 4 times 2, times negative 5, end root, and denominator 2 times 2, end fraction. This can be rewritten as x equals, the fraction with numerator 2 plus or minus the square root of 44, end root, and denominator 4 . Since the square root of 44 equals, the square root of 2 squared, times 11, end root, or 2 times the square root of 11, the equation can be rewritten as x equals, the fraction with numerator 2 plus or minus 2 times the square root of 11, end root, and denominator 4. Dividing 2 from both the numerator and denominator yields the fraction with numerator 1 plus the square root of 11, end root, and denominator 2 or the fraction with numerator 1 minus the square root of 11, end root, and denominator 2. Of these two solutions, only the fraction with numerator 1 plus the square root of 11, end root, and denominator 2 is present among the choices. Thus, the correct choice is D.

Choice A is incorrect and may result from a computational or conceptual error. Choice B is incorrect and may result from using x equals, the fraction with numerator negative b plus or minus the square root of b squared, minus 4 a c, end root, and denominator a, end fraction instead of x equals, the fraction with numerator negative b, plus or minus the square root of b squared, minus 4 a c, end root, and denominator 2 a, end fraction as the quadratic formula. Choice C is incorrect and may result from rewriting the square root of 44 as 4 times the square root of 11 instead of 2 times the square root of 11.