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.

Directly proportional: as one amount increases, another amount increases at the same rate.It's the relation between quantities whose ratio is constant.

In an inverse proportion, the two variables are inversely proportional to one another. One can write this equation as y = k/x, where K is the constant of proportionality that relates the two variable. In this equation as X increases, Y decreases.