What's x (x-9) = 10?

a) x = 20, x = - 2

b) x = 65, x = - 56

c) x = - 10, x = 1

d) x = 10, x = - 1

Hi Laysia

x (x - 9) = 10

x² - 9x = 10

x² - 9x - 10 = 0

Factor left side

(x + 1) (x-10)

Now we can set the factors equal to 0

x + 1 = 0 or x - 10 = 0

x = 0 - 1 or x = 0 + 10

x = - 1 or x = 10

Answer : x - 1 or x = 10

The correct option is : D

Let me know if you have any further questions.

Expand and put them all on one side in decreasing order of degree of x:

x^2 - 9x - 10 = 0

-9 = 1 - 10

-10 = 1 * (-10)

so (x+1) (x-10) = 0

So

x+1=0

(x = - 1)

And

x-10=0

(x=10)

So the solutions are 10 and - 1 which is d.