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unit 2 homework question - HSN forum

# unit 2 homework question

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### #1claribell

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Posted 08 January 2007 - 05:05 PM

A curve for which dy/dx = 3x² + 1 passes through the point (-1,2)
Express y in terms of x.

im sure it is probably a simple question but i dont know how to do it. can anyone help me? thanks

### #2loved-up-loon

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Posted 08 January 2007 - 05:19 PM

Integrate the dy/dx part (remembering the +C), so you will be left with an equation startin y=... Then to find out C, sub in the point your given.

(I think thats how you do it, not 100% sure though)
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### #3claribell

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Posted 08 January 2007 - 05:21 PM

QUOTE(loved-up-loon @ Jan 8 2007, 05:19 PM)

Integrate the dy/dx part (remembering the +C), so you will be left with an equation startin y=... Then to find out C, sub in the point your given.

(I think thats how you do it, not 100% sure though)

thank you makes sense now

### #4claribell

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Posted 08 January 2007 - 05:40 PM

y=∫dy/dx (dx)
=∫3x² + 1
=3x³/3 + x + c
=x³ + x + c

sub in (-1,2)

2=(-1³) + (-1) + c
2=(-1) - 1 + c
2= -2 + c
-2 + c = 2
c = 2 + 2
c= 4

so y=x³ + x + 4

can anyone tell me if that is right?

### #5Gillz

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Posted 08 January 2007 - 05:57 PM

As far as i can see that is correct. I did a similar question the other day.

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Posted 08 January 2007 - 06:25 PM

Yup it's right
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### #7claribell

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Posted 08 January 2007 - 09:17 PM

thank you

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