really? For a second i thought i misspoke when i tried to do it myself. Good on you if you found it.
Here is a shorter way if you know the arithmetic-geometric mean inequality:
\(\displaystyle \displaystyle \frac{a_1+a_2+\cdots +a_n}{n} \ge \sqrt[n]{a_1a_2\cdots a_n}\)
then
\(\displaystyle \displaystyle \frac{2a+b}{3} = \frac{a+a+b}{3} \ge \sqrt[3]{a\cdot a\cdot b} = \sqrt[3]{a^2b}\)
yeah this is a very good way thank you so much and i m sorry for disturbance
can i ask another question?
yes, that looks good, but the proof should be written backwards, unless you turn the implications into double-implications: \(\displaystyle \iff\)