已知25a2-10a+1+|4b+1|=0,求[(4a+3b)(4a-3b)-(2a-5b)(8a+5b)]÷(-2b).

问题描述:

已知25a2-10a+1+|4b+1|=0,求[(4a+3b)(4a-3b)-(2a-5b)(8a+5b)]÷(-2b).

∵25a2-10a+1+|4b+1|=0,∴(5a-1)2+|4b+1|=0,
∴a=

1
5
、b=
1
4

∴[(4a+3b)(4a-3b)-(2a-5b)(8a+5b)]÷(-2b)
=(16a2-9b2-16a2+25b2+30ab)÷(-2b)
=(16b2+30ab)÷(-2b)
=-8b-15a
=-8×(-
1
4
)-15×
1
5

=2-3
=-1.