Question

Tìm a , b , c biết rằng

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

Answer 1

a/2=b/3 nên a/10=b/15

b/5=c/4 nên b/15=c/12

=>a/10=b/15=c/12

Áp dụng tính chất của dãy tỉ số bằg nhau, ta được:

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

Do đó: a=-70; b=-105; c=-84

Answer 2

\(\dfrac{a}{2}=\dfrac{b}{3}=>\dfrac{1}{5}.\dfrac{a}{2}=\dfrac{1}{5}.\dfrac{b}{3}=>\dfrac{a}{10}=\dfrac{b}{15}\left(1\right)\\ \dfrac{b}{5}=\dfrac{c}{4}=>\dfrac{1}{3}.\dfrac{b}{5}=\dfrac{1}{3}.\dfrac{c}{4}=>\dfrac{b}{15}=\dfrac{c}{12}\left(2\right)\)

\(\left(1\right),\left(2\right)=>\dfrac{a}{10}=\dfrac{b}{15}=\dfrac{c}{12}=\dfrac{a-b+c}{10-15+12}=\dfrac{-49}{7}=-7\\ =>a=\left(-7\right).10=-70;b=\left(-7\right).15=-105;c=\left(-7\right).12=-84\)