Question

(c+9d)^2−(9c+d)^2 Разложи на множители

Answer 1

$(c+9d)^2-(9c+d)^2=c^2+18cd+81d^2-81c^2-18cd-d^2=\\=-80c^2+80d^2=-80(c^2-d^2)=-8\cdot10\cdot(c-d)(c+d)=(-8c+8d)(10c+10d)$