若(3a-9)^2与|a-b+1|互为相反数.求(2a^2-3ab+6b^2)-1/2(3a^2-ab+96^2)的值?

问题描述:

若(3a-9)^2与|a-b+1|互为相反数.求(2a^2-3ab+6b^2)-1/2(3a^2-ab+96^2)的值?

(3a-9)^2+|a-b+1|=0(3a-9)^2=0,|a-b+1|=0解得a=3b=4(2a^2-3ab+6b^2)-1/2(3a^2-ab+9b^2)=2a^2-3ab+6b^2-3a^2/2+ab/2-9b^2/2=2a^2-3a^2/2-3ab+ab/2+6b^2-9b^2/2=a^2/2-5ab/2+3b^2/2=3^2/2-5*3*4/2+3*4^2/2=9/2-30+24...先化简,再计算。