ruse question 9 2003 trial (1 Viewer)

[scarvesss]

can somebody help me out with the last part of (b). idk why but i am lost when solving for L'=0



the equation in the solutions that i got to that needs to be simplified is:

 

[Leffife]

What about it?

You know the chain rule? Just apply it.

 

[Sy123]

From there cross multiply, you will get cubic terms and a quartic terms, however they will cancel out. You are left with the quadratic, which you can then factorise into x=5/3 and 15

Then you either can use real world logic, or test either sides of the two points to check for minimum, you find out x=5/3 minimum

There are your 7 marks

Lazy question....

 

[scarvesss]

ugh yeh sorry i think i just saw the big equations and just disregarded being able to do it. thanks anyway