Question

(2ax + bx)2

Answer 1

You'd have to distribute the 2 to your whole equation.
2ax*2=4ax
bx*2=2bx

So now you have 4ax+2bx.

Answer 2

\[(2ax+bx)^2=(2ax+bx)(2ax+bx)\]
Compare to
\[(u+v)^2=u^2+2uv+v^2\]

Answer 3

I'm assuming the 2 at the end was an exponent and not multiplication.