x Turn on thread page Beta
 You are Here: Home >< Maths

# Differentiation equations of tangents watch

1. Find the equation of the tangent to the curve at the point with he given x-coordiante.

y=x^2 where x=-1

I can find the equations normally when im given a pair of coordinates but here i only know x is -1 so im not sure what to do any help?
2. (Original post by hazbaz)
Find the equation of the tangent to the curve at the point with he given x-coordiante.

y=x^2 where x=-1

I can find the equations normally when im given a pair of coordinates but here i only know x is -1 so im not sure what to do any help?
What is y when x is -1?
3. well y = x^2 so...
4. Ah right ye my bad so Y is equal to 1
5. (Original post by hazbaz)
Find the equation of the tangent to the curve at the point with he given x-coordiante.

y=x^2 where x=-1

I can find the equations normally when im given a pair of coordinates but here i only know x is -1 so im not sure what to do any help?
When x=-1, y=1 by plugging it into y=x^2.
Now differentiate to find the gradient at that point. Then express your line in whatever form you are used to i.e. y=mx+c or (y-y1)=m(x-x1) and substitute x1 and y1 as the x and y-values from above because the tangent must pass through that point.
6. (Original post by Farhan.Hanif93)
When x=-1, y=1 by plugging it into y=x^2.
Now differentiate to find the gradient at that point. Then express your line in whatever form you are used to i.e. y=mx+c or (y-y1)=m(x-x1) and substitute x1 and y1 as the x and y-values from above because the tangent must pass through that point.

Ye so i have the point (-1,1)

and diffrentiate to get y=2x

at the point (-1,1) x = -1

I worked out the gradient of the tangent to be -2

So using Y=Mx+C Y=-2x+C

at the point (-1,1) 1= -1 +C so i got C =2 therefore the equation is

Y= -2x+2 but the book says the asnwer is Y=-2x -1 where have i gone wrong?

I worked it out i didnt use teh tangent gradient in the Y=Mx+C
7. (Original post by hazbaz)
So using Y=Mx+C Y=-2x+C

at the point (-1,1) 1= -1 +C so i got C =2 therefore the equation is

Y= -2x+2 but the book says the asnwer is Y=-2x -1 where have i gone wrong?
The bit that I've highlighted in red is wrong... note that y=-2x+C and not y=x+C.

EDIT: Oh you noticed. Never mind.
8. (Original post by hazbaz)
Ye so i have the point (-1,1)

and diffrentiate to get y=2x

at the point (-1,1) x = -1

I worked out the gradient of the tangent to be -2

So using Y=Mx+C Y=-2x+C

at the point (-1,1) 1= -1 +C so i got C =2 therefore the equation is

Y= -2x+2 but the book says the asnwer is Y=-2x -1 where have i gone wrong?

I worked it out i didnt use teh tangent gradient in the Y=Mx+C
At the point (-1,1), x=-1 and y=1 so you need to plug those values into y=-2x+c so you get 1=2 + c, what is c?
9. (Original post by nuodai)
The bit that I've highlighted in red is wrong... note that y=-2x+C and not y=x+C.

EDIT: Oh you noticed. Never mind.
Yep thanks for helping though

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: September 26, 2010
Today on TSR

### How much will your degree earn you?

Find out where yours ranks...

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams