已知a2-b2=0,且ab≠0,求分式a2-3ab+5b2/3a2-2ab+4b2的值.
问题描述：
已知a2-b2=0,且ab≠0,求分式a2-3ab+5b2/3a2-2ab+4b2的值.
答
(a2-3ab+5b2) / (3a2-2ab+4b2 ) = [(a^2 - b^2) + 6b^2 - 3ab] / [3(a^2 - b^2) + 7b^2 - 2ab] = [6b^2 - 3ab] / [7b^2 - 2ab] = [6b - 3a] / [7b - 2a] (1) a+b = 0 ==> [6b - 3a] / [7b - 2a] = [6b+ 3b] / [7b + ...