You are Here: Home

# Higher Maths: Optimisation watch

1. Hey,
I've been trying to get this optimisation question.
I've got the answer to (b), but cannot for the love of me get part (a)

Could someone give me some hints as to how you get it?

Thanks!
Attached Images

2. try to get the height in terms of x.

if you're still struggling:
Spoiler:
Show
inner surface area = 2 sides + 2 sides + bottom
12=2(2xh)+2(xh) + 2x^2

then V=lbh
3. For part b, do you just differentiate?
4. (Original post by Dado Prso)
try to get the height in terms of x.

if you're still struggling:
Spoiler:
Show
inner surface area = 2 sides + 2 sides + bottom
12=2(2xh)+2(xh) + 2x^2

then V=lbh
Hey,
I managed to get the surface area earlier... but just can't work out the next bit
Still can't get it How I hate the first bit of these questions!
5. (Original post by CT_Scan)
For part b, do you just differentiate?
Yeah, then nature table.
6. (Original post by FuturePilot)
Yeah, then nature table.

Yeah, thanks for reassuring me. I am sorry but I cannot help you with the first part, have you had your prelim yet? Mines is tomorrow.
7. Part b:

Differentiate

Nature Table

Equate to 0

Then Solve

Methinks
8. (Original post by FuturePilot)
Hey,
I managed to get the surface area earlier... but just can't work out the next bit
Still can't get it How I hate the first bit of these questions!
rearrange the surface area equation to get (6-x^2)/3x=h

v=lbh
v=2x^2 x (6-x^2/3x)

v=2x^2/3x x (6-x^2)

v=2x/3 (6-x^2) as required.
9. (Original post by CT_Scan)
Yeah, thanks for reassuring me. I am sorry but I cannot help you with the first part, have you had your prelim yet? Mines is tomorrow.
No bother. Oh, good luck! Mine's on Friday
10. Could someone help me with this one?

f(x) = 4x^2 - 14x +24

It was in our prelim and we had to find the answer which minimizes the function.

I think I did it the right way but I don't know if I got the right answer?
11. (Original post by Lulope)
Could someone help me with this one?

f(x) = 4x^2 - 14x +24

It was in our prelim and we had to find the answer which minimizes the function.

I think I did it the right way but I don't know if I got the right answer?
f'(x) = 8x - 14

f'(x) = 0 at sps,
8x = 14
x = 7 / 4

(this is clearly going to be the minimum, since there aren't any other sps!)

f(7 / 4) = 4(49/16) - 14(7/4) + 24 = 49 / 4 - 49 / 2 + 24 = 0.25(49 - 98 + 96) = 47 / 4

is the minimum tp of f.

(The way you've worded it sounds like you only needed x = 7 / 4 as the answer, though)
12. (Original post by TheUnbeliever)
f'(x) = 8x - 14

f'(x) = 0 at sps,
8x = 14
x = 7 / 4

(this is clearly going to be the minimum, since there aren't any other sps!)

f(7 / 4) = 4(49/16) - 14(7/4) + 24 = 49 / 4 - 49 / 2 + 24 = 0.25(49 - 98 + 96) = 47 / 4

is the minimum tp of f.

(The way you've worded it sounds like you only needed x = 7 / 4 as the answer, though)
Thank you!

I have a horrible feeling I integrated instead of differentiating
13. -differentiate and make equal to zero for x.
-find the second derivative (so differentiate again)
-substitute in x to the second derivative and if your answer is negative, it gives a Maximum
.
14. 7 years later ... they have probs got their degree now hahah

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 13, 2017
The home of Results and Clearing

### 2,915

people online now

### 1,567,000

students helped last year
Today on TSR

### University open days

1. London Metropolitan University
Sat, 18 Aug '18
2. Edge Hill University
Sat, 18 Aug '18
3. Bournemouth University
Sat, 18 Aug '18
Poll
Applying to university

Our tool will help you find the perfect uni course for you

Study Help rules and posting guidelines

## Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE