\(C=\left(a+2\times b\right)+\left(b+2\times c\right)+\left(x+2\times a\right)\)
\(\Leftrightarrow C=a+b+c+2\times b+2\times c+2\times a\)
\(\Leftrightarrow C=\left(a+b+c\right)+2\left(a+b+c\right)\)
\(\Leftrightarrow C=\left(a+b+c\right)\left(2+1\right)=15.3=45\)
\(C=\left(a+2\times b\right)+\left(b+2\times3\right)+\left(c+2\times a\right)\)
\(C=a+2\times b+b+2\times c+c+2\times a\)
\(C=\left(a+b+c\right)+\left(2a+2b+2c\right)=15+2\left(a+b+c\right)\)
\(=15+2\times15=15+30=45\)
Ta có :
\(C=\left(a+2\times b\right)+\left(b+2\times c\right)+\left(c+2\times a\right)\)
\(=a+2\times b+b+2\times c+c+2\times a\)
\(=\left(a+b+c\right)+\left(2\times b+2\times c+2\times a\right)\)
\(=\left(a+b+c\right)+2\times\left(a+b+c\right)\)
\(=\left(a+b+c\right)\times\left(1+2\right)\)
\(=\left(a+b+c\right)\times3\)
Thay \(a+b+c=15\)vào biểu thức trên có :
\(C=15\times3\)
\(C=45\)
Vậy C = 45 khi a+b+c = 15 .
Học tốt
