已知:A=5a2+3,B=3a2-2a2b,C=a2+6a2b-2,求a=-1,b=2时,求A-2B+C的值.
问题描述:
已知:A=5a2+3,B=3a2-2a2b,C=a2+6a2b-2,求a=-1,b=2时,求A-2B+C的值.
答
A-B+C=(5a2+3)-2(3a2-2a2b)+(a2+6a2b-2)
=5a2+3-6a2+4a2b+a2+6a2b-2
=(5a2-6a2+a2)+(4a2b+6a2b)+(3-2)
=10a2b+1,
当a=-1,b=2时,10a2b+1=10×(-1)2×2+1=21.