[(3a-2b)(3a+2b)-(a+2b)(5a-2b)]÷4a
=[3a²-4b²-5a²-8ab+4b²]÷4a
=（-2a²-8ab）÷4a
=-1/2a-2b
因为 a=(1/2)^0,b=-1^-1
a=0
b=-1
原式就=2
祝学习进步