Question

If A=20 and A= x * (x-1), then?

Answer 1

A= 20
A = x*(x-1) which means...
20 =x*(x-1) now solve for x by expanding the brackets,

20 = x^2 - x  convert this into quadratic equation..

x^2 - x - 20 = 0 
Factorise >> (x+4)(x-5)

hence there could be two values for x 
x= - 4 or x = 5 

Hope this helps!!

Answer 2

We know that A= 20

A= x*(x-1)

20= x(x-1)

20= x^2-x

Subtract x^2 from both sides

20-(x^2-x)= x^2-x-(x^2-x)

-x^2+x+20=0

Factor left sides of equation

(-x-4)(x-5)=0

Set factors equal to 0

-x-4=0 or x-5=0

x = -4 or x= 5

I hope that's help !