A=x2+xy-y2,B=-x2-2xy+y2,当x=1,y=1时,求2a-b的值x2代表x的二次方y2等也代表二次方
问题描述：
A=x2+xy-y2,B=-x2-2xy+y2,当x=1,y=1时,求2a-b的值
x2代表x的二次方
y2等也代表二次方
答
4
答
2a-b=2（x2+xy-y2）-（-x2-2xy+y2）
=2x2+2xy-2y2+x2+2xy-y2
=3x2+4xy-3y2
=3+4-3
=4
答
2A-B
=2（x²+xy-y²）-(-x²-2xy+y²)
=2x²+2xy-2y²+x²+2xy-y²
=3x²+4xy-3y²
=3*1²+4*1*1-3*1²
=3+4-3
=4