How do you solve #x^2-x=90#?
On the left, we have what appears to be a quadratic, so we can set it equal to zero to find its roots.
We can subtract
To factor this business on the left, let's do a little thought experiment:
What two numbers sum up to
After some trial and error, we arrive at
To solve from here, we can use the Zero Product Property. If the product of two things is equal to zero, one or both of those things must be equal to zero.
Let's set both of them equal to zero to get
Hope this helps!