7класс ^-^ algebra 1,21 - х²= 144 - 49n²= (a-2)²(a+2)²= (5x - 2y)²-9y²= (2a+b)²- (a-2b)²= (4p-q)²-(2p+3q)²=

1,21-х^2=(1,1-х)(1,1+х)

144-49n^2=(12-7n)(12+7n)

(а-2)^2 - (а+2)^2=(а-2-а-2)(а-2+а+2)= -4*2а= -8а

(5х-2у)^2-9у^2=(5х-2у-3у)(5х-2у+3у)=5(х-у)(5х+у)

(2a+b)^2-(a-2b)^2=(2a+b-a+2b)(2a+b+a-2b)=(a+3b)(3a-b)

(4p-q)^2-(2p+3q)^2=(4p-q-2p-3q)(4p-q+2p+3q)=(2p-4q)(6p+2q)=4(p+2q)(3p+q)

дополн. 3
(а-2)^2(а+2)^2=а^4+4а^3+4а^2 -4а^3 -16а^2 -16а+4а^2+16а+16=а^4 -8а^2 +16