a)
4x^2-25
b)
81-(2x+1)^2
źródło:
4x^2-25=(2x-5)(2x+5)
81-(2x+1)^2=[9-(2x+1)][9+(2x+1)]=
=(9-2x-1)(9+2x+1)=(8-2x)(10+2x)=
=-2(-4+x)*2(5+x)=-4(x-4)(x+5)