Answer
$5y-4$
Work Step by Step
Step 1: The formula to be used here is, $(a+b)(a-b)= a^{2}-b^{2}$,
Step 2: Applying the formula to the expression in the question , $(\sqrt (5y) +2)(\sqrt (5y)-2)$ = $(\sqrt (5y))^{2}- (2)^{2}$
Step 3: Simplifying, $(\sqrt (5y))^{2}- (2)^{2}$= $5y-4$
