algebra help

Question

If (a,−20) is a point on the graph of y=x^2−9x, what is a?

Answer 1

Hy jessica, 

 

a^2 -9a = -20

 

a^2 -9a + 20 = 0

 

(a-5)(a-4) = 0

 

a = 5 and a = 4

 

Good luck with the rest of your problems. 

 

Regards, 

 

Mayuran 

Answer 2

What you have (a,-20) simply means that you substitute a in place of x and -20 in place of y.

 

You then have to solve that quadratic equation in a.