7 Класс
(q-p)(q+p)=
(a-c)(c+a)=
(y-5)(y+5)=
(1-a)(1+a)=
(2x-3y)(2x+3y)=
(5x+3y)(3y-5x)=

q²+pq-pq-p²=q²-p²ac+a²-c²-ac=a²-c²y+5y-5y-25=y²-251+a-a-a²=1-a²4x+6xy-6xy-9y²=4x²-9y²15xy-25x²+9y²-15xy=-25x²+9y²