a)−2(3a+5b)+3(4b−6a)=−6a−10b+12b−18a=−6a−18a−10b+12b=−24a+2b
b)−7(x−3y+71z−2)−3(y+x+z)−18y=−7x−7⋅(−3y)−7⋅71z−7⋅(−2)−3y−3x−3z−18y=−7x+21y−z+14−3y−3x−3z−18y=
=−7x−3x+21y−3y−18y−z−3z+14=−10x−4z+14
c)2(21a+0,25b)−4(1,25a−43b)−a+b=2⋅21a+2⋅0,25b−4⋅1,25a−4⋅(−43b)−a+b=a+0,5b−5a+3b−a+b=
=a−5a−a+0,5b+3b+b=−5a+4,5b
d)−31(2,1x2−451y2)+y2+5x2+6(32y2−131x2)=−31⋅2,1x2−31⋅(−451y2)+y2+5x2+6⋅32y2+6⋅(−131x2)=
=−31⋅1021x2+31⋅521y2+y2+5x2+4y2+6⋅(−34x2)=−107x2+57y2+y2+5x2+4y2−8x2=
=−107x2+5x2−8x2+57y2+y2+4y2=−3107x2+5y2+152y2=−3,7x2+652y2=−3,7x2+6104y2=−3,7x2+6,4y2
