Question

( x + 1) + ( x+ 4 ) + ( x + 7 ) + (x + 10 ) + ............ + ( x + 28 ) = 155

71 + 65 x 4 = x + 140_x + 260

Answer 1

a) \(\left(x+1\right)+\left(x+4\right)+\left(x+7\right)+...+\left(x+28\right)=155\)

    \(\Rightarrow10\times x+\left(1+4+7+...+28\right)=155\)  

     \(\Rightarrow10\times x+\frac{\left(1+28\right)\times10}{2}=155\)

      \(\Rightarrow10\times x+145=155\)

       \(\Rightarrow10\times x=10\Rightarrow x=1\)

b) 

Answer 2

có ai giải được phần b ko

Answer 3

b, 71 + 65 x 4 = x + 140 _x + 260

71 + 260 =( x + 140) : x + 260

71 = (x + 140) : x

70 ^x x : x = x+ 140

70 ^x x = 140

x = 140 : 70

x=2