Question

7a=9b=21c và a-b+c=15. Khi đó (a+b-c)²=...

Answer 1

\(7a=9b=21c=\frac{a}{\frac{1}{7}}=\frac{b}{\frac{1}{9}}=\frac{c}{\frac{1}{21}}\) Áp dụng TC DTSBN ta có :

\(\frac{a}{\frac{1}{7}}=\frac{b}{\frac{1}{9}}=\frac{c}{\frac{1}{21}}=\frac{a-b+c}{\frac{1}{7}-\frac{1}{9}+\frac{1}{21}}=\frac{15}{\frac{5}{63}}=189\)

\(\Rightarrow a=27;b=21;c=9\)

\(\Rightarrow\left(a+b-c\right)^2=\left(27+21-9\right)^2=1521\)

Answer 2

cho 3 so tu nhien co uoc chung la 12. 3 so do ti le nghich voi 4;6;15. so lon nhat la