已知丨2a+3b-7丨+(a-9b+7)^2=0,试求(1/4a²-1/2ab+b^2)(1/2a+b)的值.

丨2a+3b-7丨+(a-9b+7)^2=0
则：2a+3b-7=0
a-9b+7=0
解得：a=2,b=1
(1/4a²-1/2ab+b^2)(1/2a+b)=(a/2-b)²/(a/2+b)=0