Cobby's Methods Questions

[cobby]

Hey all,
would someone please answer this question for me?



Determine the rule for the following cubic functions with these points.
a) (-1,3) and (4,0)
    Where (-1,3) is a point of zero gradient

b) (-1,0) (0,-24) and (3,0)

Thanks

[kurrymuncher]

a) sub (-1,3) and (4,0) into the equation y=ax^3 + bx^2 + cx + d, . Then derive ax^3 + bx^2 + cx + d and sub in (-1,3)


b) use the general cubic equation and sub the coordinates in

[cobby]

a) sub (-1,3) and (4,0) into the equation y=ax^3 + bx^2 + cx + d, . Then derive ax^3 + bx^2 + cx + d and sub in (-1,3)


b) use the general cubic equation and sub the coordinates in

for A) am i meant to have 3 eq's in the end? :S and do i solve them simultaneously afterwards?

[kurrymuncher]

Yes

[Edmund]

For the first,

Differentiate the general cubic equation to get 3ax^2 + 2bx + c

So,

3ax^2 + 2bx + c = 0 because zero gradient

Sub in (-1,3)

You should get one equation from here.



(Yep, 3 equations and is a pain :S)

[cobby]

ok for part a)
the answer i got was

a = (-25c+6)/175 
b = 50c-9/175
d = 4(25c+132)/175

Can someone please confirm these results?

[/0]

ok for part a)
the answer i got was

a = (-25c+6)/175 
b = 50c-9/175
d = 4(25c+132)/175

Can someone please confirm these results?

a = -(25c+6)/175, b = (50c-9)/175, d is correct.

This is most likely a calculator question, the way I would do it is define , define , then
solve(f(-1)=3 and f(4)=0 and g(-1)=0,{a,b,d})

[Mao]

this most likely won't appear on an exam

[cobby]

Hey all ive got another question


 Use a graphic calc to determine the co-ordinates of the turning points correct to two decimal places.
How do i do that?

Thanks

[dekoyl]

Hey all ive got another question


 Use a graphic calc to determine the co-ordinates of the turning points correct to two decimal places.
How do i do that?

Thanks

2nd >> Trace >> 4 (maximum)
Get the cursor on the left of the maximum turning point (left bound) which is near x = 0. ENTER
Get the cursor on the right of the maximum turning point (right bound) which is near x = 0. ENTER.
Press ENTER again.
Should get x = -0.305 and y = .486 to three decimal places (not sure how many they want)

Repeat this for the minimum turning point.

[GerrySly]

Should get x = -0.305 and y = .486 to three decimal places (not sure how many they want)

Use a graphic calc to determine the co-ordinates of the turning points correct to two decimal places.[/cobby]

[cobby]

Hey all ive got another question


 Use a graphic calc to determine the co-ordinates of the turning points correct to two decimal places.
How do i do that?

Thanks

2nd >> Trace >> 4 (maximum)
Get the cursor on the left of the maximum turning point (left bound) which is near x = 0. ENTER
Get the cursor on the right of the maximum turning point (right bound) which is near x = 0. ENTER.
Press ENTER again.
Should get x = -0.305 and y = .486 to three decimal places (not sure how many they want)

Repeat this for the minimum turning point.

Thanks for the dekoyl
I think we are using different calcs? Because i had to use F5Math : Minimum and Maximum.
But still the same cursor movements to get the values. 

[dekoyl]

Thanks for the dekoyl
I think we are using different calcs? Because i had to use F5Math : Minimum and Maximum.
But still the same cursor movements to get the values. 

Ah yes we probably do.
I did non-CAS so, yeah.
Glad that you got it.

[plato]

Hey all ive got another question


 Use a graphic calc to determine the co-ordinates of the turning points correct to two decimal places.
How do i do that?

Thanks

2nd >> Trace >> 4 (maximum)
Get the cursor on the left of the maximum turning point (left bound) which is near x = 0. ENTER
Get the cursor on the right of the maximum turning point (right bound) which is near x = 0. ENTER.
Press ENTER again.
Should get x = -0.305 and y = .486 to three decimal places (not sure how many they want)

Repeat this for the minimum turning point.

Sorry Dekoyl but you definitely should NOT use Trace to find any of the major points with any calculator whether in Methods or Methods CAS. Each calculator will have a function somewhere that finds max/min ponts, intersections, zeroes etc.

[Mao]

Hey all ive got another question


 Use a graphic calc to determine the co-ordinates of the turning points correct to two decimal places.
How do i do that?

Thanks

2nd >> Trace >> 4 (maximum)
Get the cursor on the left of the maximum turning point (left bound) which is near x = 0. ENTER
Get the cursor on the right of the maximum turning point (right bound) which is near x = 0. ENTER.
Press ENTER again.
Should get x = -0.305 and y = .486 to three decimal places (not sure how many they want)

Repeat this for the minimum turning point.

Sorry Dekoyl but you definitely should NOT use Trace to find any of the major points with any calculator whether in Methods or Methods CAS. Each calculator will have a function somewhere that finds max/min ponts, intersections, zeroes etc.

If you read the instructions carefully, he did give instructions for using functionality for finding max/min points.