SAT Question of the Day June 18 2013

y = (negative 2 times x^2) + (b times x) + 5

In the xy-plane, the graph of the equation above assumes its maximum value at x = 2. What is the value of b?

A.     negative 8

B.     negative 4

C.     4

D.     8

E.     10

We have a quadratic equation (X to the 2nd). The X coordinate of the vertex (where the quadratic equation obtained its max or min value) is determined by X=(-b)/(2a) where b is the number coefficient of the X and a is the number coefficient of the X^2

b=? a=(-2) and we know X=2

plugging in we have: 2=(-b)/[2*(-2)]

or 2=(-b)/(-4)

-8=-b

or b=8

You can also use your TI calculator to plug numbers in and find, using the min/max functions which value satisfies the conditions – but this is much more difficult.

36% out of 145,000 got it right.

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