HELP! Calculator problems.

[geoff_821]

SO I'm already frustrated at todays exam.
I'm doing EXAM 2 VCAA 2007, Extended Response Question 1.

1a. I Found h correctly
b. I found the Area correctly.
c. It asks for the value of r, in terms of V, so the area of the can is a minimum.
From b. Area = (2V)/r + 2(pi)(r)^2
I put that into my calculator to find dA/dr
= 4(pi)r-(2V)/r^2

In order to find a minimum you let dA/dr = 0, and I solved this using my CAS calculator.
The answer (V/(2(pi))^1/3
but when I put it into my calculator I get: ((2^2/3)V^1/3))/2(pi)^2/3

I was angry at the time and chucked it all into my calculator coz I couldn't be bothered.
I understand how to work it out by hand, BUT WHY ISNT MY STUPID CALCULATOR GIVING ME THE RIGHT ANSWER 
So

[geoff_821]

Okay I just found out that they give the same answers, but how? I don't understand how they equal eachother

[geoff_821]

Okay nevermind, all is solved.
However question 1d. Can someone tell me why they use V^1/3/10 as the radius?
Seeing as it's the lower bound, wouldn't that give a minimum total surface area, rather than a maximum?

[RossiJ]

that's an interest conversation you just had with yourself

[mickeymouse]

Okay nevermind, all is solved.
However question 1d. Can someone tell me why they use V^1/3/10 as the radius?
Seeing as it's the lower bound, wouldn't that give a minimum total surface area, rather than a maximum?

yeah i got that wrong too, its the endpoint and gives the maximum, cos the minimum you worked out before right in the previous question

[geoff_821]

Okay nevermind, all is solved.
However question 1d. Can someone tell me why they use V^1/3/10 as the radius?
Seeing as it's the lower bound, wouldn't that give a minimum total surface area, rather than a maximum?

yeah i got that wrong too, its the endpoint and gives the maximum, cos the minimum you worked out before right in the previous question

Why don't we use the other endpoint.
It seems illogical that they're using the lowest endpoint for the radius, rather than the largest.
Wouldn't the largest radius give you a higher area.
VCAA need to expand on their solutions -.-

[mickeymouse]

Okay nevermind, all is solved.
However question 1d. Can someone tell me why they use V^1/3/10 as the radius?
Seeing as it's the lower bound, wouldn't that give a minimum total surface area, rather than a maximum?

yeah i got that wrong too, its the endpoint and gives the maximum, cos the minimum you worked out before right in the previous question

Why don't we use the other endpoint.
It seems illogical that they're using the lowest endpoint for the radius, rather than the largest.
Wouldn't the largest radius give you a higher area.
VCAA need to expand on their solutions -.-

yeah that was what I was thinking, but if you sub in the other end point value,
it actually gives a much smaller surface area O_O

[geoff_821]

Okay nevermind, all is solved.
However question 1d. Can someone tell me why they use V^1/3/10 as the radius?
Seeing as it's the lower bound, wouldn't that give a minimum total surface area, rather than a maximum?

yeah i got that wrong too, its the endpoint and gives the maximum, cos the minimum you worked out before right in the previous question

Why don't we use the other endpoint.
It seems illogical that they're using the lowest endpoint for the radius, rather than the largest.
Wouldn't the largest radius give you a higher area.
VCAA need to expand on their solutions -.-

yeah that was what I was thinking, but if you sub in the other end point value,
it actually gives a much smaller surface area O_O

ohh wtf. fuck it.
fuck tha police

[mickeymouse]

Okay nevermind, all is solved.
However question 1d. Can someone tell me why they use V^1/3/10 as the radius?
Seeing as it's the lower bound, wouldn't that give a minimum total surface area, rather than a maximum?

yeah i got that wrong too, its the endpoint and gives the maximum, cos the minimum you worked out before right in the previous question

Why don't we use the other endpoint.
It seems illogical that they're using the lowest endpoint for the radius, rather than the largest.
Wouldn't the largest radius give you a higher area.
VCAA need to expand on their solutions -.-

yeah that was what I was thinking, but if you sub in the other end point value,
it actually gives a much smaller surface area O_O

ohh wtf. fuck it.
fuck tha police

LOL don't worry about it
maybe stop studying, wake tomorrow and smash exam 2