Whats the correct answer?

Question

Jacob determined the zeroes of a quadratic function to be -7 and 3. Which expression can be used to represent this function?

A.x²+10x–21

B.x²–7x+3

C.x²+4x-21

D.x2+3x-7

Answer 1

Hey Jalixa,

The zeroes being -7 and 3 can be written as X=-7 and X=3.

for X=-7 add 7 to both sides to get (X+7)=0. For X=3 subtract 3 from both sides to get (X-3)=0

Now multiply the two binomials: (X+7)(X-3) using FOIL to get x^2+4x-21.

So your answer is C.

Hope this helps.

michael r.

Answer 2

Since the question gives the zeroes of the equation, we can quickly get to the factors of the equation:

             For Zero = -7, the factor is: (x + 7)           (When x = -7, the factor = 0)

             For Zero = 3, the factor is: (x – 3)             (When x = 3, the factor = 0)

From the factors, we can get the equation:

             f(x) = (x + 7)(x – 3)

                   = x² + 4x – 21