Tìm a,b,c biết:
a/\(\dfrac{a}{2}=\dfrac{b}{3}=\dfrac{c}{5}\)và a.b.c=810
b/\(\dfrac{a}{4}=\dfrac{b}{3}=\dfrac{c}{9}\)và \(a-3b+4c=62\)
c/\(\dfrac{2a}{3}=\dfrac{3b}{4}=\dfrac{4c}{5}\)và a+b+c=49
d/\(\dfrac{a}{b}=\dfrac{9}{7}\)và\(\dfrac{b}{c}=\dfrac{7}{3}\),a-b+c=15