SAT Question of The Day June 27th 2013

y = (x^2) minus (4 times x) + c)

In the quadratic equation above, c is a constant. The graph of the equation in the x y plane contains the points (minus 2 comma 0) and(6 comma 0). What is the value of c?

A.     negative 12

B.     negative 6

C.     4

D.     6

E.     12

Well – this is a nice question as you are actually given too much information.

We have the equation that correlates between X values and Y values.

This relation is quadratic. We are missing the value of a number that is replaced by the letter C.

It is clear that if the relation between X and Y is true then C must assumes a certain value.

The graph of the equation passes through 6,0 that implies that when X=6 Y=0

0=6^2-4*6+C or 0=36-24+C

That in turn means C=-12

You could have come to the same conclusion using the other point – however – if you don’t like to work hard try to avoid negative numbers.

52% out of 143,000 got it right.

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