Question

Tìm x biết: ( x x 1 ) + ( x x 2 ) + ( x x 3 ) +.....+ ( x x 9 ) = 405

Answer 1

\(\left(x\times1\right)+\left(x\times2\right)+...+\left(x\times9\right)=405\)

\(\Rightarrow x\left(1+2+3+...+9\right)=405\)

\(\Rightarrow x\times45=405\)

\(\Rightarrow x=405:45\)

\(\Rightarrow x=9\)

Answer 2

Xyz sao mình tính được là 405:50 là có dư

Answer 3

( X x 1 ) + ( X x 2 ) + ( X x 3 ) +.....+ ( X x 9 ) = 405

X x ( 1 + 2 +3 + .....+ 9 ) = 405

X x 45 = 405

    X     = 405: 45 

    X     =  9

Answer 4

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Answer 5

\(\left(x\times1\right)+\left(x\times2\right)+...+\left(x\times9\right)=405\)

=> \(x\left(1+2+3+...+9\right)=405\)

=>\(x\times45=405\)

=> \(x=9\)

Hok tot

Answer 6

(x . 1) + (x . 2) + (x . 3) + ... + (x . 9) = 405

<=> x . 1 + x .2 + x . 3 + ... + x . 9 = 405

<=> x(1 + 2 + 3 + ... + 9) = 405

<=> x . 45 = 405

<=> x = 405/45 = 9