[(3a-2b)(3a+2b)-(a+2b)(5a-2b)]÷4a
=[3a²-4b²-5a²-8ab+4b²]÷4a
=（-2a²-8ab）÷4a
=-1/2a-2b
其中a=2,b=-3
原式 = - 1/2 x 2 + 2x3
= - 1 + 6
= 5