SAT Nonlinear equations in one variable and systems of equations in two variables Practice Question 13 (Medium)

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Question bank / Nonlinear equations in one variable and systems of equations in two variables

Math · Advanced MathMedium

What are the solutions to the equation $x^2 + 8x = 9$ ?

$-9$ and $1$

$9$ and $-1$

$-8$ and $0$

$-3$ and $3$

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Answer: A

Subtract 9 to set the equation equal to zero: $x^2 + 8x - 9 = 0$ . Factor: $(x + 9)(x - 1) = 0$ . So $x = -9$ or $x = 1$ .

Choice C comes from factoring $x(x + 8) = 9$ and setting each factor equal to 0, which only works when the other side is 0.

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