Giải câu 3 trang 102 sách toán VNEN lớp 6 tập 1

a) (2600 + 6400) - 3.x = 1200 $\Rightarrow$ 9000 - 3.x = 1200 $\Rightarrow$ 3.x = 7800 $\Rightarrow$ x = 2600;                 

b) [(6.x - 72) : 2 - 84] .28 = 5628 $\Rightarrow$ (6.x - 72) : 2 - 84 = 201 $\Rightarrow$ (6.x - 72) : 2 = 285

                                                    $\Rightarrow$ 6.x - 72 = 570 $\Rightarrow$ 6.x = 642 $\Rightarrow$ x = 107; 

c) 2x - 138 = 2$^{3}$.3$^{2}$ $\Rightarrow$ 2x - 138 = 72 $\Rightarrow$ 2x = 210 $\Rightarrow$ x = 105;                         

d) 42x = 39.42 - 37.42 $\Rightarrow$ 42x = 42.(39 - 37) $\Rightarrow$ x = 39 - 37 $\Rightarrow$ x = 2.