Question

Упростите выражение:

Answer 1

$3(y+5)^2-3y^2=3\cdot \Big (\underbrace {(y+5)^2-y^2}_{A^2-B^2}\Big )=\\\\=[\, A^2-B^2=(A-B)(A+B)]=\\\\=3\cdot (y+5-y)(y+5+y)=3\cdot 5\cdot (2y+5)=15\cdot (2y+5)$