Hello, scottie.mcdonald!

The third one requires a "simple" substitution . . .

Let: .

. . Then: .

Substitute: .

. .

Back-substitute: . .[1]

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

We could stop here, but we can simplify the answer further . . .

Multiply the fracton by

. .

Then [1] becomes: .

. . . . . . . . . . . .

. . . . . . . . . . . .

Pull something like this on any of your exams,

. . and I'll guarentee that you'll surprise/impress/terrify your teacher.