Giải thích các bước giải:
$2)\\ a)3(2a-1)+5(3-a)\\ =6a-3+15-5a\\ =a+12\\ a=-\dfrac{3}{2} \Rightarrow a+12=-\dfrac{3}{2}+12=\dfrac{21}{2}\\ b)25x-4(3x-1)+7(5-2x)\\ =25x-12x+4+35-14x\\ =-x+39\\ x =2,1 \Rightarrow -x+39=-2,1+39=36,9\\ c)4a-2(10a-1)+8a-2\\ =4a-20a+2+8a-2\\ =-8a\\ a=-0,2 \Rightarrow -8a=-8.(-0,2)=\dfrac{8}{5}\\ d)12(2-3b)+35b-9(b+1)\\ =24-36b+35b-9b-9\\ =-10b+15\\ b=\dfrac{1}{2} \Rightarrow -10b+15=-10.\dfrac{1}{2}+15=-5+15=10$
