a) x + 5 = 2015 – (12 – 7)
x +5 =2015-5
x + 5 =2010
x =2010-5
x =2005
b) |x-5| = 11
⇔\(\left[ \begin{array}{1}x=11\\x=-11\end{array} \right.\)
TH1:x-5=11
x =11+5
x =16
TH2:x-5=-11
x =-11+5
x =-6
c)2^(x -1) = 8
2^(x -1) = 2^3
x–1=3x–1=3
`x = 3 + 1
x=4