Đáp án:
`a,x=18;x=-21`
`b,x=7;x=-7`
Giải thích các bước giải:
`a,(x+1)(x+2)=380`
`⇔x^2+2x+x+2=380`
`⇔x^2+3x-378=0`
`⇔x^2+21x-18x-378=0`
`⇔(x^2+21x)-(18x+378)=0`
`⇔x(x+21)-18(x+21)=0`
`⇔(x-18)(x+21)=0`
⇔\(\left[ \begin{array}{l}x-18=0\\x+21=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=18\\x=-21\end{array} \right.\)
Vậy `x=18;x=-21`
`b,(2^2.|x|-5^2).3^8=3^9`
`⇔2^2.|x|-5^2=3^9:3^8`
`⇔4|x|-25=3`
`⇔4|x|=28`
`⇔|x|=7`
`⇔x=±7`
Vậy `x=7;x=-7`
