先化简,再求值:(a²-2ab+b²分之2a-2b+a²-b²分之b)÷a-b分之3b+2a,其中a=5,b=2

先化简,再求值:(a²-2ab+b²分之2a-2b+a²-b²分之b)÷a-b分之3b+2a,其中a=5,b=2
先化简,再求值:(a²-2ab+b²分之2a-2b+a²-b²分之b)÷a-b分之3b+2a,其中a=5,b=2

先化简,再求值:(a²-2ab+b²分之2a-2b+a²-b²分之b)÷a-b分之3b+2a,其中a=5,b=2
原式=[2(a-b)/(a-b)²+b/(a+b)(a-b)]×(a-b)/(2a+3b)
=[2/(a-b)+b/(a+b)(a-b)]×(a-b)/(2a+3b)
=[(2a+2b+b)/(a+b)(a-b)]×(a-b)/(2a+3b)
=(2a+3b)/(a+b)(a-b)×(a-b)/(2a+3b)
=1/(a+b)
=1/(5+2)
=1/7