\(a,VT=\left(a+b-c\right)+\left(a-b+c\right)\)
\(=a+b-c+a-b+c\)
\(=\left(a+a\right)+\left(b-b\right)+\left(-c+c\right)\)
\(=2a=VP\)
\(b,VT=\left(a-b-c\right)-\left(a-b+c\right)\)
\(=a-b-c-a+b-c\)
\(=\left(a-a\right)+\left(-b+b\right)+\left(-c-c\right)\)
\(=-2c=VP\)
\(c,VT=\left(a+1\right)-\left(b+c+1\right)+\left(b-a+2\right)\)
\(=a+1-b-c-1+b-a+2\)
\(=\left(a-a\right)+\left(-b+b\right)+\left(1-1+2\right)-c\)
\(=2-c=VP\)
\(d,VT=-a-\left(2-b-c\right)+\left(1-b-c-a\right)\)
\(=-a-2+b+c+1-b-c-a\)
\(=\left(-a-a\right)+\left(b-b\right)+\left(c-c\right)+\left(-2+1\right)\)
\(=-2a-1=VP\)
#Toru
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