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B) 7 (-2x+4y-5z)-(-3x-5y+6z) -2 (5x-3y+9z).

Resursa: a (b+c) = a×b+a×c.


Răspuns :

7 (-2x+4y-5z)-(-3x-5y+6z) -2 (5x-3y+9z). =

= -14x +28y -35z - 
(-3x-5y+6z) -2 (5x-3y+9z). = 

= -14x +28y -35z + 3x +5y -6 x - 10x +6y -18z =

= -21x + 28y -35z + 5y -6z + 6y -18z =

= -21x + 39y -35z -6z -18z =

=  -21x + 39y -59z