a)= \(\dfrac{15}{34}+\dfrac{1}{3}+\dfrac{19}{34}-\dfrac{49}{17}+\dfrac{2}{3}\)
= \(\left(\dfrac{15}{34}+\dfrac{19}{34}\right)+\left(\dfrac{1}{3}+\dfrac{2}{3}\right)\)\(-\dfrac{49}{17}\)
= 1 + 1 \(-\dfrac{49}{17}\)
= \(2+\dfrac{49}{17}=\dfrac{34}{17}+\dfrac{49}{17}=\dfrac{83}{17}\)
b) = -(10,92 + 2,85) + 10,92 - ( 2 - 2,85)
= (-10,92 +10,92) + ( 2,85 - 2,85 ) - 2
= 0 + 0 - 2
= -2