Question

Покажите тождество
(7х-2)^2 -(7х-1)×(7х+1)=-28+5

Answer 1

$(7x-2)^2 -(7x-1)cdot(7x+1)=49x^2-28x+4-(49x^2-1)=\\49x^2-28x+4-49x^2+1=-28x+5$