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`c, 25-(x-5) = -415 - (15 - 415)`
`25-(x-5) = -415 - 15 + 415`
`25-(x-5 )= ( 415 - 415 ) - 15`
`25-(x-5)= 0 - 15`
`25-(x-5) = -15`
`x-5 = 25 - (-15)`
`x-5 = 40`
`x=40+5`
`x=45`
Vậy ` x = 45`
`f, (x-3)(2x+6)=0`
`\(\left[ \begin{array}{l}x-3=0\\2x+6=0\end{array} \right.\)
\(\left[ \begin{array}{l}x=3\\2x=-6\end{array} \right.\)
\(\left[ \begin{array}{l}x=3\\x=-3\end{array} \right.\)
Vậy ` x ∈ { 3 ; -3 }`
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