若a-b/b=1/2,则3a2-5ab+2b22a2+3ab-5b2的值是_.

问题描述:

a-b
b
=
1
2
,则
3a2-5ab+2b2
2a2+3ab-5b2
的值是___

3a2-5ab+2b2
2a2+3ab-5b2

=
(3a-2b)(a-b)
(2a+5b)(a-b)

=
3a-2b
2a+5b 

a-b
b
=
1
2

∴a=
3
2
b,
∴原式=
9
2
b-2b
3b+5b
=
5
16

故填空答案:
5
16