\(\left(2x+3\right)\left(2x-3\right)=4x^2-9\)
\(\left(a^2+5\right)\left(5-a^2\right)=25-a^4\)
( 2x + 3 ) ( 2x - 3 )
= [ ( 2x )2 + 6x ] - ( 6x + 9 )
= ( 2x )2 + ( 6x - 6x ) + 9
= ( 2x )2 + 9
( a2 + 5 ) ( 5 - a2 )
= ( 5a2 + 25 ) - ( a4 + 5a2 )
= ( 5a2 - 5a2 ) + 25 - a4
= 25 - a4