a) (5+2x)(2x-5) + 25
= 5(2x) + 5(-5) + 2x(2x) + 2x(-5) + 25
= 10x - 25 + 4x^2 - 10x + 25
= 4x^2

б) 4(7-2a)-(a-4)(2^c)
= 28 - 8a - (a-4)2^c
= 28 - 8a - 2^ca + 2^c4
= 32 - 8a - 2^c*a