Question

x + 2x+3x+...+9x =990

Tìm x

Answer 1

\(x+2x+3x+....+9x=990.\)

\(\Rightarrow x.\left(1+2+3+....+9\right)=990\)

\(\Rightarrow x.45=990\)

\(\Rightarrow x=990:45\)

\(\Rightarrow x=22\)

Answer 2

X duoc xuat hien so lan la:

            1+2+3+4+5+6+7+8+9=45

x=990÷45=22

                 ĐS:22

Answer 3

x + 2x + 3x + ... + 9x = 990
   ( 1 + 2+ 3 + ... + 9 ) . x = 990
   45 . x = 990
   x = 990 : 45
   x = 22

Answer 4

Ta có:   x + 2x + 3x +...+ 9x = 990

\(\Leftrightarrow\)(1 + 2 +3 +...+ 9)x = 990

\(\Leftrightarrow\)45x = 990

\(\Leftrightarrow\)x = 990/45 = 22

Vậy x = 22

Answer 5

x + 2x+3x+...+9x  = 990

1x + 2x+3x+...+9x = 990

x .(1+2+3+...+9)     =  990

Đặt A = 1 + 2 + 3 +...+9 (có 9 số hạng)

A= (1+9) . 9 : 2

A = 10. 9 : 2

A = 45

=> x . 45 = 990

    x         =  990 : 45

     x        = 22

Vậy x = 22

Answer 6

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