Question

已知a=5x的平方y-3xy的平方+4xy,b=7xy的平方-2xy+x的平方y.

求a－2b 求－2分之1﹙a＋b﹚－a

Answer 1

a-2b
=(5x²y-3xy²+4xy)-2(7xy²-2xy+x²y)
=5x²y-3xy²+4xy-14xy²+4xy-2x²y
=3x²y+8xy-17xy²

－2分之1﹙a＋b﹚－a
=-1/2a-1/2b-a
=-3/2a-1/2b
自己代入进去试试看能不能算出

Answer 2

解
a=5x²y-3xy²+4xy
b=7xy²-2xy+x²y
∴
a-2b
=(5x²y-3xy²+4xy)-2(7xy²-2xy+x²y)
=(5x²y-2x²y)+(-3xy²-14xy²)+(4xy+4xy)
=3x²y-17xy²+8xy

-1/2(a+b)-a
=-1/2a-a-1/2b
=-3/2a-1/2b
=-3/2(5x²y-3xy²+4xy)-1/2(7xy²-2xy+x²y)
=(-15/2x²y-1/2x²y)+(9/2xy²-7/2xy²)+(-6xy+xy)
=-8x²y+xy²-5xy