Efectuati calculele:
a) (x-2)(x+2)+(x-3)(x+3)+(x-4)(x+4)+(x-5)(x+5)=
b)(a-3)(a+3)+(a-3)²=
c)(m+5)²-(m+5)(m-5)=
a) (x-2)(x+2)+(x-3)(x+3)+(x-4)(x+4)+(x-5)(x+5)=