Áp dụng t/c dãy tỉ số bằng nhau ta có:
\(\frac{1}{a+b+c}=\frac{a+4b-c+b+4c-a+c+4a-b}{a+b+c}\)
\(=\frac{4\left(a+b+c\right)}{a+b+c}=4\)
\(\Rightarrow\left\{{}\begin{matrix}4c=a+4b-c\\4a=b+4a-a\\4b=c+4a-b\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}5c=a+4b\\5a=b+4c\\5b=c+4a\end{matrix}\right.\)
\(\Rightarrow a=b=c\)
\(P=\left(2+\frac{a}{b}\right)\left(3+\frac{b}{c}\right)\left(4+\frac{c}{a}\right)\)
\(=\left(2+1\right)\left(3+1\right)\left(4+1\right)\)
\(=3.4.5=60\)
Vậy .............
Cái đề thiếu dấu " = " kìa -__-
