Question

(a+5). (a-5)-(a+5)^2

Answer 1

$\mathrm{(a+b)(a-b)=a^2-b^2}\\ \mathrm{(a+b)^2=a^2+2ab+b^2}\\\\ \mathrm{(a+5)(a-5)-(a+5)^2=}\\ \mathrm{=a^2-5^2-(a^2+2.a.5+5^2)=}\\ \mathrm{=a^2-5^2-a^2-10a-5^2=}\\ \mathrm{=-10a-2.5^2=-10a-2.25}\\ \mathbf{=-10a-50}$