(a+b)^7

Remember, GL.....we can distribute an exponent over this (a * b)⁷.......but not this (a + b)⁷

The second thing says to multiply (a + b)  seven times......

$${\left({\mathtt{a}}{\mathtt{\,\small\textbf+\,}}{\mathtt{b}}\right)}^{{\mathtt{7}}}$$

Distribute.

$${{\mathtt{a}}}^{{\mathtt{7}}}{\mathtt{\,\small\textbf+\,}}{{\mathtt{b}}}^{{\mathtt{7}}}$$

That's as far as can be simplified, I'm afraid.

And then there's CPhill...