a) \(30+\left(-30\right)+7\)
\(=30-30+7\)
\(=0+7\)
\(=7\)
b) \(12+\left(-31\right)\)
\(=12-31\)
\(=-31+12\)
\(=-\left(31-12\right)\)
\(=-19\)
c) \(\left(-40\right)+\left(-20\right)+\left(-40\right)\)
\(=-40-20-40\)
\(=-\left(40+20\right)-40\)
\(=-60-40\)
\(=-\left(60+40\right)\)
\(=-100\)
d) \(13+\left|-13\right|\)
\(=13+13\)
\(=26\)
e) \(\left|-13\right|+\left|-12\right|+\left|-17\right|\)
\(=13+12+17\)
\(=25+17\)
\(=42\)
f) \(-17+\left|-17\right|+12\)
\(=-17+17+12\)
\(=-\left(17-17\right)+12\)
\(=-0+12\)
\(=-\left(0-12\right)\)
\(=-\left(-12\right)\)
\(=12\)
a, = 7
b, = -19
c, = -100
d, = 26
e, = 42
f, = 12
f) (x – 5)2 = 9 
