合并同类项:-a的2次方+2a的2次方;x-2x+3/2x+1/2X;-ab+2ba-5ab;2m的平方n-3+5m的平方n；y-2(y+3)
问题描述：
合并同类项:-a的2次方+2a的2次方;x-2x+3/2x+1/2X;-ab+2ba-5ab;2m的平方n-3+5m的平方n；y-2(y+3)
答
-a的2次方+2a的2次方
=a²
x-2x+3/2x+1/2X
=(1-2+1.5+0.5)x
=x
-ab+2ba-5ab
=(-1+2-5)ab
=-4ab
2m的平方n-3+5m的平方n
=7m²n-3
y-2(y+3)
=y-2y-6
=-y-6