Question

C = (a+2xb)+(b+2xc)+(c+2xa)

Với a+b+c=15    

Mình cần gấp .    

 

Answer 1

\(C=\left(a+2\times b\right)+\left(b+2\times c\right)+\left(x+2\times a\right)\)

\(\Leftrightarrow C=a+b+c+2\times b+2\times c+2\times a\)

\(\Leftrightarrow C=\left(a+b+c\right)+2\left(a+b+c\right)\)

\(\Leftrightarrow C=\left(a+b+c\right)\left(2+1\right)=15.3=45\)

Answer 2

\(C=\left(a+2\times b\right)+\left(b+2\times3\right)+\left(c+2\times a\right)\)

\(C=a+2\times b+b+2\times c+c+2\times a\)

\(C=\left(a+b+c\right)+\left(2a+2b+2c\right)=15+2\left(a+b+c\right)\)

\(=15+2\times15=15+30=45\)

Answer 3

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 .

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