Resposta:
a)
\begin{gathered}\begin{array}{rcl}\left(+\dfrac{1}{9}\right)+\left(-\dfrac{2}{9}\right) &=& \dfrac{1}{9}-\dfrac{2}{9} \\ &=& -\dfrac{1}{9}\end{array}\end{gathered}
(+
9
1
)+(−
9
2
)
=
=
9
1
−
9
2
−
9
1
b)
\begin{gathered}\begin{array}{rcl}(-9{,}6)-(-2{,}5) &=& -9{,}6+2{,}5 \\ \\ &=& -7{,}1 \end{array}\end{gathered}
(−9,6)−(−2,5)
=
=
−9,6+2,5
−7,1
c)
\begin{gathered}\begin{array}{rcl}\left(-\dfrac{7}{30}\right)+\left(+\dfrac{4}{30}\right)+\left(-\dfrac{11}{30}\right) &=& -\dfrac{7}{30}+\dfrac{4}{30}-\dfrac{11}{30} \\ \\ &=& \dfrac{-7+4-11}{30} \\ \\ &=& -\dfrac{14}{30} \\ \\ &=& -\dfrac{7}{15} \end{array}\end{gathered}
(−
30
7
)+(+
30
4
)+(−
30
11
)
=
=
=
=
−
30
7
+
30
4
−
30
11
30
−7+4−11
−
30
14
−
15
7
d)
\begin{gathered}\begin{array}{rcl}(-4{,}1)+(-15{,}2) &=& -4{,}1-15{,}2 \\ \\ &=& -19{,}3 \end{array}\end{gathered}
(−4,1)+(−15,2)
=
=
−4,1−15,2
−19,3
e)
\begin{gathered}\begin{array}{rcl}\left(+\dfrac{2}{3}\right)+\left(-\dfrac{1}{8}\right) &=& \dfrac{2}{3}-\dfrac{1}{8} \\ \\ &=& \dfrac{2\cdot 8}{3\cdot 8} -\dfrac{1\cdot 3}{8\cdot 3} \\ \\ &=& \dfrac{16}{24}-\dfrac{3}{24} \\ \\ &=& \dfrac{13}{24}\end{array}\end{gathered}
(+
3
2
)+(−
8
1
)
=
=
=
=
3
2
−
8
1
3⋅8
2⋅8
−
8⋅3
1⋅3
24
16
−
24
3
24
13
f)
\begin{gathered}\begin{array}{rcl}\left(-\dfrac{1}{5}\right)-\left(+\dfrac{2}{3}\right)+\left(-\dfrac{1}{4}\right) &=& -\dfrac{1}{5}-\dfrac{2}{3}-\dfrac{1}{4}\\ \\ &=&-\dfrac{1\cdot 3\cdot 4}{5\cdot 3\cdot 4}-\dfrac{2\cdot 5\cdot 4}{3\cdot 5\cdot 4}-\dfrac{1\cdot 5\cdot 3}{4\cdot 5\cdot 3} \\ \\ &=& -\dfrac{12}{60}-\dfrac{40}{60}-\dfrac{15}{60}\\ \\ &=& \dfrac{-12-40-15}{60} \\ \\ &=&- \dfrac{67}{60} \end{array}\end{gathered}
(−
5
1
)−(+
3
2
)+(−
4
1
)
=
=
=
=
=
−
5
1
−
3
2
−
4
1
−
5⋅3⋅4
1⋅3⋅4
−
3⋅5⋅4
2⋅5⋅4
−
4⋅5⋅3
1⋅5⋅3
−
60
12
−
60
40
−
60
15
60
−12−40−15
−
60
67
Espero ter ajudado ^3^
