Two numbers have a sum of 9 and a product of 20.

What single-variable quadratic equation in the form ax^2 + bx + c = 0 can be used to represent the product of the two numbers?

Question

Two numbers have a sum of 9 and a product of 20.

What single-variable quadratic equation in the form ax^2 + bx + c = 0 can be used to represent the product of the two numbers?

campbell_st · Answer

a + b = 9   (1)

ab = 20      (2)

looking at equation (1) it can be rewritten as a = 9 - b

substitute it into equation (2)

b(9 -b) = 9b - b^2

so your quadratic is  -b^2 + 9b

anonymous · Answer

I have a really hard time with questions like these, do you have any tips?

campbell_st · Answer

nope... just read it carefully the write you equations and try to fins an easy substitution

in the question above I forgot to finish it

should be 

-b^2 + 9b - 20 = 0