5x-6=7 1+2+3+4+5+6+7+8+9....+15

2 câu trả lời

Đáp án:

$5x$ $-$ $6$ $=$ $7$
$5x$ $=$ $7$ $+$ $6$ 
$5x$ $=$ $13$
$x$ $=$ $\frac{13}{5}$ 

$1$  $+$  $2$  $+$  $3$  $+$ $4$  $+$  $5$  $+$  $6$  $+$  $7$  $+$  $8$  $+$  $9$  $....$  $+$ $15$
$=$  $( 1 + 15 )$ $×$ $15$ $:$ $2$
$=$  $16$ $×$ $15$ $:$ $2$
$=$  $8$  $×$  $15$
$=$  $120$
@cloudie

`5x-6=7`

`->5x=7+6`

`->5x=13`

`->x=\frac{13}{5}`

Vậy `x=\frac{13}{5}`

$\\$

`1+2+3+4+5+...+15`

`=(1+15)+(2+14)+(3+13)+...+(7+9)+8`

`=16+16+16+16+16+16+16+8`

`=16xx7+8`

`=112+8`

`=120`