intergration question Watch

djmans
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for this question i wanted to know if i need to find C when integrating, i checked the marking scheme and it showed C but they never found C in the answer.
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TobyReichelt
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You're given the bounds--this means you can ignore C, because you have numbers to work with.
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Name:  CodeCogsEqn.gif
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Sub in the values for X.
Remember F(a)-F(b).
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Zacken
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(Original post by djmans)
for this question i wanted to know if i need to find C when integrating, i checked the marking scheme and it showed C but they never found C in the answer.
You use +c when you're integrating without limits and you don't use +c when you are integrating with limits.

This makes, sense, because if you want to integrate something between limits, you do \int_1^2 x \, \mathrm{d}x, this gets you (let's include the constant to show you why it's useless):

\displaystyle \bigg[ \frac{x^2}{2} + c \bigg]_1^2 = \frac{2^2}{2} + c - \frac{1^2}{2} - c = \frac{4 - 1}{2}

that is, when there are limits, the constants will always cancel, so you don't need to put them there in the first place.
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M14B
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(Original post by djmans)
for this question i wanted to know if i need to find C when integrating, i checked the marking scheme and it showed C but they never found C in the answer.
You cannot find C
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TobyReichelt
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(Original post by TobyReichelt)
You're given the bounds--this means you can ignore C, because you have numbers to work with.
Spoiler:
Show
Name:  CodeCogsEqn.gif
Views: 123
Size:  1.5 KB
Sub in the values for X.
Remember F(a)-F(b).
Please ignore that image. I forgot to actually do the integration.
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djmans
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(Original post by Zacken)
You use +c when you're integrating without limits and you don't use +c when you are integrating with limits.

This makes, sense, because if you want to integrate something between limits, you do \int_1^2 x \, \mathrm{d}x, this gets you (let's include the constant to show you why it's useless):

\displaystyle \bigg[ \frac{x^2}{2} + c \bigg]_1^2 = \frac{2^2}{2} + c - \frac{1^2}{2} - c = \frac{4 - 1}{2}

that is, when there are limits, the constants will always cancel, so you don't need to put them there in the first place.
thx i got it now
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djmans
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(Original post by Zacken)
You use +c when you're integrating without limits and you don't use +c when you are integrating with limits.

This makes, sense, because if you want to integrate something between limits, you do \int_1^2 x \, \mathrm{d}x, this gets you (let's include the constant to show you why it's useless):

\displaystyle \bigg[ \frac{x^2}{2} + c \bigg]_1^2 = \frac{2^2}{2} + c - \frac{1^2}{2} - c = \frac{4 - 1}{2}

that is, when there are limits, the constants will always cancel, so you don't need to put them there in the first place.
one more thing, these types of questions with a limit are always integration?
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Zacken
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(Original post by djmans)
one more thing, these types of questions with a limit are always integration?
Yes.
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djmans
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(Original post by Zacken)
Yes.
in questions how do i identify if i must differentiate or integrate?
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WhisperingTide
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"Using calculus!"

Did the next question ask you to 'Do the thing!!!"

If they want a question to be particularly open ended and challenging do they just say: "You might want to use some kind of method or something."? :P

Sorry, that tickled me far too much.
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WhisperingTide
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(Original post by djmans)
in questions how do i identify if i must differentiate or integrate?
Every question will tell you, in one way or another.

Typically, if you need to find a gradient, you differentiate, if you need to find an area, you integrate.

The big, elongated 'S' looking thing means you need to integrate. If you see something like d/dx or f'(x) (after being given f(x)) you need to differentiate, in general.
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EricPiphany
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(Original post by WhisperingTide)
"Using calculus!"

Did the next question ask you to 'Do the thing!!!"

If they want a question to be particularly open ended and challenging do they just say: "You might want to use some kind of method or something."? :P

Sorry, that tickled me far too much.
Calculators with numerical integrators are allowed in lots of exams.
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WhisperingTide
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(Original post by EricPiphany)
Calculators with numerical integrators are allowed in lots of exams.
Yeah, I know why it makes sense, but that doesn't stop me from finding it funny.
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EricPiphany
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(Original post by WhisperingTide)
Yeah, I know why it makes sense, but that doesn't stop me from finding it funny.
That's good.
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djmans
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if its f'(x) what should i do?
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Zacken
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(Original post by djmans)
if its f'(x) what should i do?
If you integrate f'(x) you get f(x)+ c. Then you use the given point to find c.
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Kevin De Bruyne
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(Original post by djmans)
if its f'(x) what should i do?
What is the rest of the question? Find f(x) in terms of x? Given a set of co-ordinates, you can work out what c is.
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B_9710
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(Original post by djmans)
if its f'(x) what should i do?
Integrate to find y.
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djmans
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(Original post by Zacken)
If you integrate f'(x) you get f(x)+ c. Then you use the given point to find c.
so f its f'(x) i must integrate
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Zacken
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(Original post by djmans)
so f its f'(x) i must integrate
Essentially, yeah...
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