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`