Question

please sopve my problem

Answer 1

here identity ( a+b) (a-b) is used
so,
$= (5 {x}^{2} + \frac{3}{4} {y}^{2} )(5 {x}^{2} - \frac{3}{4} {y}^{2} )$
$= (5 {x}^{2}) {}^{2} - (\frac{3}{4} {y}^{2} ) {}^{2}$
$= 25 {x}^{4 } - \frac{9}{16 } {y}^{4}$

Answer 2

now this is correct because of the formula which given in side