Freaky Things That Can Happen 1

We've been solving nice guys like

x^2 - 3x - 18 = 0
Notice that it's already set equal to 0.

So, what if the problem starts out like this?

Can we just factor and do the blob thing?

So x = 18 or x - 3 = 18 which gives x = 21

Are these the answers? Check them!

x = 18: x^2 - 3x - 18 = 0 which gives ( 18 )^2 - 3 ( 18 ) - 18 = 0 which gives 324 - 54 - 18 = 0 ... No way!

Why didn't this work?

Think about our main idea"

If a * b = 0 , then a = 0 or b = 0

IT MAKES SENSE!

But, THIS is what we tried:

If a * b = 18 , then a = 18 or b = 18

WE CANNOT SAY THIS!

Uh.... What about

There are a ton of things a and b can be other than 18.

So, when you start with something like

ALWAYS SET IT = 0 FIRST.
ALWAYS!

Finish it!

YOUR TURN:

Solve

Freaky Things That Can Happen with Quadratics