Answer
$x^{2a}-y^{4b}$
Work Step by Step
Using $(a+b)(a-b)=a^2-b^2$ or the product of the sum and difference of like terms and using the laws of exponents, the given expression, $
(x^a+y^{2b})(x^{a}-y^{2b})
$, is equivalent to
\begin{array}{l}\require{cancel}
(x^{a})^2-(y^{2b})^2
\\\\=
x^{2a}-y^{4b}
.\end{array}
