Question

\(\frac{a}{2}=\frac{b}{3};\frac{b}{5}=\frac{c}{4}vàa-b+c=-49\)

Answer 1

\(\Rightarrow\)\(\frac{a}{10}=\frac{b}{15};\frac{b}{15}=\)\(\frac{c}{12}\)

\(\Leftrightarrow\frac{a}{10}=\frac{b}{15}=\frac{c}{12}\)

\(\Rightarrow\frac{a-b+c}{10-15+12}\frac{-49}{-7}=-7\)

\(\Rightarrow a=10.-7=-70\)

\(b=15.-7=-105\)

\(c=12.-7=-84\)

Answer 2

ta có \(\frac{a}{2}=\frac{b}{3}\Rightarrow\frac{a}{10}=\frac{b}{15};\frac{b}{5}=\frac{c}{4}\Rightarrow\frac{b}{15}=\frac{c}{12}\Rightarrow\frac{a}{10}=\frac{b}{15}=\frac{c}{12}=\frac{a-b+c}{10-15+12}=\frac{-49}{7}=-7\)

\(\frac{a}{10}=-7\Rightarrow a=-7.10=-71\)

\(\frac{b}{15}=-7\Rightarrow b=-7.15=-105\)

\(\frac{c}{12}=-7\Rightarrow c=-7.12=-84\)

Answer 3

\(\frac{a}{2}=\frac{b}{3};\frac{b}{5}=\frac{c}{4}\Rightarrow\frac{a}{2}=\frac{5b}{15};\frac{3b}{15}=\frac{c}{4}\Rightarrow\frac{a}{10}=\frac{b}{15}=\frac{c}{12}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có : 

\(\frac{a}{10}=\frac{b}{15}=\frac{c}{12}=\frac{a-b+c}{10-15+12}=-\frac{49}{7}=-7\)

Suy ra : \(\frac{a}{10}=-7\Rightarrow a=-7.10=-70\)

\(\frac{b}{15}=-7\Rightarrow b=-7.15=-105\)

\(\frac{c}{12}=-7\Rightarrow c=-7.12=-84\)