1.
-2,8a+5b( -1/7)= - 2.8a-5b/7= - 19.6a-5b
1 7x/9*( -0.25y)*4.5z= - 16x*0.25y*4.5z/9= - 18/9 xyz= - 2xyz
2.
-(a+2.1b)+(3.8a-1.9b)= -a-2.1b+3.8a-1.9b=2.8a-4b
3 1/3*(0.3y-0.6)-1 1/4*(0.8-1.6y)=4/3*3y/10-4/3*6/10-5/4*8/10+5/4*16y/10=2y/5-4/5-2/5+2y=2.4y-0.4
3.
1 2x/3-4(1x/24+1)=1 2x/3-x/6-4=1 3x/6-4=1 x/2-4=1.5x-4
4.
12a-2(2a+3b)=12a-4a-6b=8a-6b=2(4a-3b)
если 4a-3b=2, то
2*2=4