2道因式分解.公式法.

1/7(x-y)^3+7(y-x)
=1/7[(x-y)^3-49(x-y)]
=1/7(x-y)[(x-y)^2-49]
=1/7(x-y)(x-y+7)(x-y-7)
16(a+2b)^2-9(a-2b)^2
=[4(a+2b)-3(a-2b)][4(a+2b)+3(a-2b)]
=(a+14b)(7a-2b)