Lời giải:
`(x-7)^{x+1}-(x-7)^{x+11}=0`
`⇒(x-7)^{x+1}(1-(x-7)^{10})=0`
`+) (x-7)^{x+1}=0`
`⇔x-7=0`
`⇔x=7`
`+) 1-(x-7)^{10}=0`
`⇔(x-7)^{10}=1`
`⇔x-7=1`
`⇔x=8`
Vậy `x=7;x=8`
`b) 3x+3x+3x+1+3x+2=117`
`⇒9x+3=117`
`⇒9x=114`
`⇒x=\frac{38}{3}`
a) Đặt `A=|x+1|+5`
Vì `|x+1|≥0⇒|x+1|+5≥5`
Dấu `=` xảy ra khi:
`x+1=0⇔x=-1`
Vậy `A_{min}=5⇔x=-1`