a) mn+mn-3m-3n=б) x-125=в)y+64=a) (2a+3)-4a-(3a-5)=б)3(x+6)-(x-6)

a)

mn+mn-3m-3n=  mn(m+n) - 3(m+n) = (m + n)(mn - 3),

б)

x-125=  (x-5)(x+5*x+5) = (x - 5)(x + 5x + 25),

в)

y+64=  (y+4)(y-4*y+4) = (y + 4)(y - 4y + 16),

a)

(2a+3)-4a-(3a-5)=  2а+3-4а-9а+30а-25 = -9а + 28а - 22,

б)

3(x+6)-(x-6) (x+6)=  3х+18-х+36 = -х + 3х + 54,

в)

(m-4)(m+3)-m=  m+3m-4m-12-m = -m - 12,

a)

12c-12d=  12*(c-d) = 12*(c - d)(c + d),

б)

-m+8m-16=  -(m-8m+16) = -(m - 4),

в)

ax-ay=  a*(x-y) = a*(x - y)(x + xy + y),

г)

bc-cb=  bc*(c-b) = bc*(c - b)(c + b),

y(y+7) (y-3) = y(y-2).

у(у-3у+7у-21) = у-2у,

у - 3у + 7у - 21у - у + 2у = 0,

6у - 21у = 0,

у * (6у - 21) = 0,

у1 = 0,    6у - 21 = 0,

              6у = 21,

              у2 = 3,5