(a-b)² = a²- 2ab + b²

(a+b)²-(a-b)²
= a² + b² +2ab - (a² + b² - 2ab)
= a² + b² +2ab -a² - b² + 2ab
= 2ab + 2ab
= 4ab

As per the law of exponents a^mxaⁿ =a^m+n
Therefore
a x a² x a³ x a⁴
=a^1+2+3+4
=a¹⁰

As per the law of exponents (aⁿ)^m = a^mxn
therefore
(a⁵)⁷ = a^7x5
=a³⁵