Bài 4:
`a,-9-x=-2`
`<=>x=-9+2`
`<=>x=-7`
`b,2x+12=3(x-7)`
`<=>2x+12=3x-21`
`<=>2x-3x=-12-21`
`<=>-x=-33`
`<=>x=33`
`c,2x^2-1=49`
`<=>2x^2=50`
`<=>x^2=25`
`<=>` \(\left[ \begin{array}{l}x=5\\x=-5\end{array} \right.\)
`d,|7-2x|=1`
`<=>` \(\left[ \begin{array}{l}7-2x=1\\7-2x=-1\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}2x=6\\2x=8\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=3\\x=4\end{array} \right.\)
