\(a,=\left[321+\left(-321\right)\right]-15+30\\ =0-15+30=-15+30=15\)
\(a,321+\left(-15\right)\) \(+30\left(-321\right)\) \(=\left[321+\left(-321\right)\right]\) \(-15+30\)
\(=0-15+30=-15+30=15\)
\(321+\left(-15\right)+30+\left(-321\right)=\left(321+-321\right)+\left(-15+30\right)=0+15=15\)
a,321+(−15)a,321+(−15) +30(−321)+30(−321) =[321+(−321)]=[321+(−321)] −15+30−15+30
=0−15+30=−15+30=15
a,321+(−15)a,321+(−15) +30(−321)+30(−321) =[321+(−321)]=[321+(−321)] −15+30−15+30
=0−15+30=−15+30=15
