Question x-f-x-
For the quadratic function , the table shows three values of and their corresponding values of . Which equation defines ?
x f x - 1 10 0 14 1 20 For the quadratic function f ,
Hard-difficulty · SAT Math · Nonlinear Functions — Quadratic graphs and vertex form. 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. The equation of a quadratic function can be written in the form , where , , and are constants. It’s given in the table that when , the corresponding value of is . Substituting for and for in the equation gives , which is equivalent to , or . It’s given in the table that when , the corresponding value of is . Substituting for and for in the equation gives , or . It’s given in the table that when , the corresponding value of is . Substituting for and for in the equation gives , which is equivalent to , or . Adding to the equation gives . Dividing both sides of this equation by gives . Since , substituting for into the equation gives . Subtracting from both sides of this equation gives . Substituting for in the equations and gives and , respectively. Since , substituting for in the equation gives , or . Subtracting from both sides of this equation gives . Dividing both sides of this equation by gives . Substituting for into the equation gives , or . Subtracting from both sides of this equation gives . Substituting for , for , and for in the equation gives , which is equivalent to , or . Therefore, defines .
Choice A is incorrect. If , then when , the corresponding value of is , not .
Choice B is incorrect. If , then when , the corresponding value of is , not .
Choice C is incorrect. If , then when , the corresponding value of is , not , and when , the corresponding value of is , not .
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