[dongonaeatu]

1. The gradient of a curve is given by dy/dx=3x-4. Find the equation of the curve given that it passes through the point (3,1)

so integrate 3x-4 so= 3x^2/2-4x. can i get rid of the 2 on the denominator?

[CD315]

(Original post by dongonaeatu)
1. The gradient of a curve is given by dy/dx=3x-4. Find the equation of the curve given that it passes through the point (3,1)

so integrate 3x-4 so= 3x^3/3-4x. can i get rid of the 3 on the denominator?

Where are you getting the 3 from?

[vinvinvin]

To integrate you increase the power by one and divide by the new power. So yes you can cancel the 3 and would therefore have y=x^3-4x+d

Don't forget to include the constant!!!!

Solve using the values you know to find d.

[Pangol]

Is your original expression supposed to be dy/dx = 3x - 4, i.e. the equationn of a straight line? If you've integrated incorrectly.

If it is supposed to be dy/dx = 3x^2 - 4, i.e. a quadratic, then yes, this gives you y = (3x^3)/3 - 4x + c. Of course you can cancel the 3s in the first term - it is just three times something divided by three.

[tamimi]

Isn't it divided by two, not three :P


You divide by the new power bro

Also, +k on the end.

[dongonaeatu]

(Original post by CD315)
Where are you getting the 3 from?

sorry, i meant 2.

is the final answer for the equation of the curve y=3x^2/2-4x-1/2

[dongonaeatu]

(Original post by tamimi)
Isn't it divided by two, not three :P


You divide by the new power bro

Also, +k on the end.

is the final answer for the equation of the curve y=3x^2/2-4x-1/2

[Pangol]

That's what I make it.

[tamimi]

(Original post by dongonaeatu)
is the final answer for the equation of the curve y=3x^2/2-4x-1/2

I believe it is Either that or we're both wrong.

[mr tim]

Yep I seem to get -1/2. You don't need to get rid of the two, just sub in your x and y values after you've integrated. Best way just in case you make a mistake in getting rid of the 2.

[dongonaeatu]

(Original post by mr tim)
Yep I seem to get -1/2. You don't need to get rid of the two, just sub in your x and y values after you've integrated. Best way just in case you make a mistake in getting rid of the 2.

thanks tim, are you good at trigonometry?

[mr tim]

(Original post by dongonaeatu)
thanks tim, are you good at trigonometry?

if you can tell me the question then I'll or someone else will tell you how to answer it.

[dongonaeatu]

(Original post by mr tim)
if you can tell me the question then I'll or someone else will tell you how to answer it.

http://www.thestudentroom.co.uk/show...260&p=37114590