a)(x-2)(x-2)+(x-3)(x+3)+(x-4)(x+4)+(x-5)(x+5)=
=(x²-2²)+(x²-3²)+(x²-4²)+(x²-5²)=
=x²-4+x²-9+x²-16+x²-25=
=4x²-13-41=
=4x²-54=
=2(2x²-27)
b)(a-3)(a+3)+(a-3)²=
=a²-3²+a²-2*a*3+3²=
=a²-9+a²-6a+9=
=2a²-6a=
=2(a²-3a).
c)(m+5)²-(m+5)(m-5)=
=m²+2*m*5-m²+5²=
=m²-10m-m²+25=
=-10m+25=
=5(-2m+5).
