# How do you solve #y^2-90=13y#?

##### 2 Answers

I used the quadratic formula, and found:

#### Explanation:

We have:

Rearrange into standard form:

Standard form has the powers of the pronumeral in decreasing order on the left and

In this case,

We often use

Substituting in the values from the equation:

Therefore:

This quadratic could also be solved by factorising.

#### Explanation:

Write as:

This is no different to a quadratic in

A quadratic in

A quadratic in

So it is rotating

Lets check the whole number factors of 90 to see if any of them give a difference of 13

The 90 is negative so the two numbers are of opposite sign.

The 13 is negative so the greater of the two is negative giving:

Condition 1 :

Condition 2:

Thus