Приведение подобных
K-E-2e-3k
21e-11p+e-p
12y-21x+12x-21y
2y-6a-12y+12a
K-y-y-2y+2k
-p+2y+3p-(-2y)
2y-6a-12y+12a

k-e-2e-3k  = -2k-3e

21e-11p+e-p  = 22e-12p

12y-21x+12x-21y  = -9y-9x

2y-6a-12y+12a  = -10y+6a

K-y-y-2y+2k  = 3k-4y

-p+2y+3p-(-2y)  = 2p+4y

2y-6a-12y+12a = -10y+6a