Question

 a,b,ca,b,c biết rằng a/2 =b/3 ,b/5 =c/4 a-b+c =21

Answer 1

\(\dfrac{a}{2}=\dfrac{b}{3}\Rightarrow\dfrac{a}{10}=\dfrac{b}{15}\)

\(\dfrac{b}{5}=\dfrac{c}{4}\Rightarrow\dfrac{b}{15}=\dfrac{c}{12}\)

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

Áp dụng tính chất dãy tỉ số bằng nhau ta có:
\(\dfrac{a}{10}=\dfrac{b}{15}=\dfrac{c}{12}=\dfrac{a-b+c}{10-15+12}=\dfrac{21}{7}=3\)

\(\dfrac{a}{10}=3\Rightarrow a=30\\ \dfrac{b}{15}=3\Rightarrow b=45\\ \dfrac{c}{12}=3\Rightarrow c=36\)

Vậy ...