Question

a/2 = b/3 = c/4 và a + 2b - 3c = ( - 20 )

Answer 1

Ta có: \(\frac{a}{2}=\frac{b}{3}=\frac{c}{4}\)

\(\Rightarrow\frac{a}{2}=\frac{2b}{6}=\frac{3c}{12}=\frac{a+2b-3c}{2+6-12}=\frac{-20}{-4}=5\)

\(\frac{a}{2}=5\Rightarrow a=5\times2=10\)

\(\frac{2b}{6}=5\Rightarrow2b=30\Rightarrow b=15\)

\(\frac{3c}{12}=5\Rightarrow3c=60\Rightarrow c=20\)

Answer 2

\(\frac{a}{2}=\frac{b}{3}=\frac{c}{4}\Rightarrow\frac{a}{2}=\frac{2b}{6}=\frac{3c}{12}\)

Áp dụng dãy tỉ số bằng nhau ta có : 

        \(\frac{a}{2}=\frac{2b}{6}=\frac{3c}{12}=\frac{a+2b-3c}{2+6-12}=-\frac{20}{-4}=5\)

=> a=  2.5 = 10 

=> b = 3.5 = 15 

=> c = 4.5 = 20