(a)
![f'(x) = \frac{d}{dx}[\frac{lnx}{x}]](https://tex.z-dn.net/?f=f%27%28x%29%20%3D%20%5Cfrac%7Bd%7D%7Bdx%7D%5B%5Cfrac%7Blnx%7D%7Bx%7D%5D)
Using the quotient rule:
For maximum, f'(x) = 0;
(b) <em>Deduce:
</em>
<em>
Soln:</em> Since x = e is the greatest value, then f(e) ≥ f(x) > f(0)
, since ln(e) is simply equal to 1
Now, since x > 0, then we don't have to worry about flipping the signs when multiplying by x.
Taking the exponential to both sides will cancel with the natural logarithmic function in the right hand side to produce:
, as required.
You are using an angle and proportional side lengths.
SAS Similarity
First you have to put all of your common numbers together. 4a and 9a go together. You then subtract those because 9 is negative (-9). Then you get -5a. Now move on to your other numbers. You have 26 and 17. 17 is negative as well (-17), so you subtract it from 26. That gives you 9.
Your new equation is -5a + 9 = 26
Now you subtract 9 from both sides. Your positive (+9) will cancel out with your negative (-9). Then subtract it from 26. 9 minus 26 is 17.
Now your equation is -5a = 17
Since it's negative, you're going to add it (5) to both sides.
Your 5's cancel out, and 17 + 5 is 22.
a = 22
22 is the answer
