\(3a^2+3b^2=10ab\)
\(\Rightarrow3a^2-10ab+3b^2=0\)
\(\Rightarrow3a^2-9ab-ab+3b^2=0\)
\(\Rightarrow\left(3a^2-9ab\right)-\left(ab-3b^2\right)=0\)
\(\Rightarrow3a\left(a-3b\right)-b\left(a-3b\right)=0\)
\(\Rightarrow\left(a-3b\right)\left(3a-b\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}a-3b=0\\3a-b=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}a=3b\\a=\dfrac{b}{3}\end{matrix}\right.\)
Hoặc Thay \(a=\dfrac{b}{3}\) vào biểu thức P ,có :
\(\dfrac{b-\dfrac{b}{3}}{b+\dfrac{b}{3}}=\dfrac{\dfrac{3b-b}{3}}{\dfrac{3b+b}{3}}=\dfrac{\dfrac{2b}{3}}{\dfrac{4b}{3}}=\dfrac{2b}{3}.\dfrac{3}{4b}\)= \(\dfrac{1}{2}\)
Vậy P =1/2
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