Any Mathematicians?

[Dav0s]

So i did an exam today, and pretty much nailed it I think..

but there was this one question that i couldnt get, and its really bothering me...

Area = 20x - 2x²

By using differentiation, find the maximum Area

This is C1 by the way, the first AS level exam. Was a retake for me...

I differentiated it, got 20-4x but now i have no idea what to do

Not sure if anybody here does actually do A level maths but its worth a shot. Big reps for anyone who can help :worship:

 

[ali_james]

Did you have something else like a value of the perimeter? 'Cos from there I think you need to find x by substituting into another value or equation.

I have C3 maths next week

 

[Dav0s]

it wasnt quite that simple.

basically the only other info you have is that the short side is x cm

and dont worry about C3, its prob the next easiest after C1. me gots 86%

 

[Dav0s]

ok i may have had a brainwave...

well when you differentiate, you get dA/dx, which is basically how fast the area is changing with respect to x.

when Area is maximum, the rate of change might be zero?

so

20 - 4x = 0

20 = 4x

x = 5

then substitute 5 back into the original equation...

20x5 - 2x25 = 100 - 50 = 50

so the maximum area is 50?

seems to sound about right, just need to check on the fact that the rate of change will be zero at the maximum area.

hands up if u understand

 

[Rastalovich]

Wouldn`t u now put 20-4x=0 and get x from that ?

(I have AS & A level LOL)

EDIT: Dav jumped in.

 

[Dav0s]

too late

yes i now realise that this method is correct, basically because at a maximum value of a function, the derivative is zero, as it is a turning point.

thanks for any help guys, i think being able to write my thoughts down helped me to understand it lol

 

[Ham]

I get it, kinda, Been about year since i did any non-computer maths though..

My teacher gave me a real simple method too do differentiation, you should asked yest.

 

[Rastalovich]

We kinda never has questions like that in the end exam.

It would be a question that ended up like that, but with something logical u had to think about before forming the equation u`rself.

 

[ali_james]

Ahh nice one it all becomes clear

Didn't have anything like that on my C1 couple of weeks back!

 

[macgamesrule]

ok i may have had a brainwave...

well when you differentiate, you get dA/dx, which is basically how fast the area is changing with respect to x.

when Area is maximum, the rate of change might be zero?

so

20 - 4x = 0

20 = 4x

x = 5

then substitute 5 back into the original equation...

20x5 - 2x25 = 100 - 50 = 50

so the maximum area is 50?

seems to sound about right, just need to check on the fact that the rate of change will be zero at the maximum area.

hands up if u understand

That is correct. Later they expand this to the second derivative.

 

[PV5150]

Yes you are correct Dave

 

[JN]

All great stuff, but the only time I ever need maths is when I want to find out if I've got enough money in my pocket for a cup of coffee and some toast first thing in the morning

 

[Oxo]

All great stuff, but the only time I ever need maths is when I want to find out if I've got enough money in my pocket for a cup of coffee and some toast first thing in the morning

second that

 

[Azreil_2]

Ooooooo... i just did my C1 and C2.. (will be retaking atleast the C2 lol)

How are C3 and C4?

 

[Dav0s]

C1: nice

C2: horrible horrible numbr crunching, formula memorising maths

C3: best module by far, get down and do some decent fun maths

C4: some nice advanced stuff which can be fun, but also some equally boring topics.

C3 is nicest, but if you like maths you will enjoy both. and on a sidenote, i hope you do enjoy maths because otherwise i wdnt bother doing it

 

[Azreil_2]

i do enjoy it, doing mechanical maths as well, just starting the c3 and the second module of mechanics

 

[Dav0s]

eugh hate mechanics and stats, nasty nasty maths

any c3 problems drop me a PM

 

[Azreil_2]

Thanks

I actually Like Mechanics