Question

Giúp mk bài 2 với ạ

Answer 1

Bài 1:

Gọi số cây 3 lớp 7A,7B,7C lần lượt là \(a,b,c\in \mathbb{N^*},cây\)

Áp dụng tc dtsbn:

\(\dfrac{a}{6}=\dfrac{b}{4}=\dfrac{c}{5}=\dfrac{a+b+c}{6+4+5}=\dfrac{30}{15}=2\\ \Rightarrow\left\{{}\begin{matrix}a=12\\b=8\\c=10\end{matrix}\right.\)

Vậy ...

Bài 3:

\(a+b\ne-c\Rightarrow a+b+c\ne0\\ \Rightarrow\dfrac{a+b-c}{c}=\dfrac{b+c-a}{a}=\dfrac{c+a-b}{b}=\dfrac{a+b+c}{a+b+c}=1\\ \Rightarrow\left\{{}\begin{matrix}a+b-c=c\\b+c-a=a\\c+a-b=b\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}a+b=2c\\b+c=2a\\c+a=2b\end{matrix}\right.\\ \Rightarrow P=\dfrac{a+b}{a}\cdot\dfrac{a+c}{c}\cdot\dfrac{b+c}{b}=\dfrac{2a\cdot2b\cdot2c}{abc}=8\)