先化简,再求2(a+b)/a-b+3b/2a+2b+ab+7b^2/2a^2-2b^2其中a=49/4,b=-31/4

先化简,再求2(a+b)/a-b+3b/2a+2b+ab+7b^2/2a^2-2b^2其中a=49/4,b=-31/4
先化简,再求2(a+b)/a-b+3b/2a+2b+ab+7b^2/2a^2-2b^2其中a=49/4,b=-31/4

先化简,再求2(a+b)/a-b+3b/2a+2b+ab+7b^2/2a^2-2b^2其中a=49/4,b=-31/4
原式=2(a+b)/(a-b)+3b/2(a+b)+(ab+7b²)/2(a+b)(a-b)
=[4(a+b)²+3b(a-b)+ab+7b²]/2(a+b)(a-b)
=(4a²+12ab+8b²)/2(a+b)(a-b)
=4(a+2b)(a+b)/2(a+b)(a-b)
=2(a+2b)/(a-b)
=2(49/4-62/4)/(49/4+31/4)
=-13/40