1.计算 [(3a-7)^2-(a+5)^2]/（4a-24),其中a=3

1.计算 [(3a-7)^2-(a+5)^2]/（4a-24),其中a=3
[(3a-7)^2-(a+5)^2]/（4a-24)
=(3a-7-a-5)(3a-7+a+5)/4(a-6)
=2(a-6)*2(2a-1)/4(a-6)
=2a-1
=6-1=5
2.已知|a+b+1|+a^2b^2+4ab+4=0,求-2a^2-2b^2的值
|a+b+1|+a^2b^2+4ab+4
=|a+b+1|+(ab+2)^2
=0
∵|a+b+1|>=0 (ab+2)^2>=0
∴a+b=-1 ab=-2
a^2+b^2=（a+b）^2-2ab=1+4=5
-2a^2-2b^2=-2(a^2+b^2)= -2*5= -10
3.已知4a^2+4a+b^2-6b^2+10=0,求ab的值
4a^2+4a+b^2-6b+10=0
4a^2+4a+1+b^2-6b+9=0
(2a+1)^2+(b-3)^2=0
a=-1/2
b=3
ab= -3/2