已知,a^2+b^2+2a-b = -5/4 ,整理得：(a+1)^2+(b-1/2)^2 = 0 ,所以,a+1 = 0 ,b-1/2 = 0 ,解得：a = -1 ,b = 1/2 .化简：原式= (a-5b)(-a-5b)-(a-5b)^2= (a-5b)[(-a-5b)-(a-5b)]= (a-5b)[-2a]= -2a^2+10ab将 a = -1 ,b...