Объяснение:

1) (3х²-2х)+(-х²+3х)=3х²-2х-х+3х=2х²+х

2) (4с²-2cd)-(10c²-8cd)=4c²-2cd-10c²+8cd=-6c²+6cd

3) (12m²-7n-3mn)-(6mn-10n-14m²)=12m²-7n-3mn-6mn+10n+14m²=

=26m²+3n-9mn

4) (3n³-2mn+4m³²)-(2mn+3n³)=3n³-2mn+4m³-2mn-3n³=4m³-2mn