multiply:

a)(2x+5)(2x-5) b) -4x^3(6x-3x^4)
show your work. please help me!!

a )

( 2 x + 5 )( 2 x - 5 ) =

2 x * 2 x + 2 x * 5 - 5 * 2 x - 5 * 5 =

4 x ^ 2 + 10 x - 10 x - 25 =

4 x ^ 2 - 25