化简多项式①3x³-（-2x³）+（-5x³）②-0.2m²n-（-1.2m²n）+3.4m²n要有过程.
问题描述：
化简多项式
①3x³-（-2x³）+（-5x³）
②-0.2m²n-（-1.2m²n）+3.4m²n
要有过程.
答
1.原式=3x³+2x³-5x³
=5x³-5x³
=0
2.原式=-0.2m²n+1.2m²n+3.4m²n
=m²n+3.4m²n
=4.4m²n
答
①3x³-（-2x³）+（-5x³）=3x³+2x³-5x³=0
②-0.2m²n-（-1.2m²n）+3.4m²n=-0.2m²n+1.2m²n+3.4m²n=4.4m²n
去括号 合并同类项
答
①3x³-（-2x³）+（-5x³）=3x³+2x³-5x³=0②-0.2m²n-（-1.2m²n）+3.4m²n=-0.2m²n+1.2m²n+3.4m²n=(-0.2+1.2+3.4)m²n=4.4m²n