已知3a-5b+19=0,a+8b-1=0,求(4a+3b)^2-8a-6b的值
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已知3a-5b+19=0,a+8b-1=0,求(4a+3b)^2-8a-6b的值
已知3a-5b+19=0,a+8b-1=0,求(4a+3b)^2-8a-6b的值
已知3a-5b+19=0,a+8b-1=0,求(4a+3b)^2-8a-6b的值
3a-5b+19=0 (1)
a+8b-1=0 (2)
(1)+(2)
4a+3b+18=0
4a+3b=-18
(4a+3b)²-8a-6b
=(4a+3b)²-2(4a+3b)
=(-18)²-2(-18)
=360
3a-5b+19=0,a+8b-1=0两式相加,得4a+3b+18=0,所以4a+3b=-18
(4a+3b)^2-8a-6=(4a+3b)^2-2(4a+3b)=(-18)²-2×(-18)=360
两式相加可得4a+3b的值
令3a-5b+19=0为(1),a+8b-1=0为(2),
(1)+(2)有4a+3b+18=0,即4a+3b=-18
所以-(8a+6b)=-2(4a+3b)=36
(4a+3b)^2-8a-6b=(-18)^2+36=360