Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    0
    ReputationRep:
    Find the equation of the normal to the curve at the point with the iven x coordinate.

    y= 1-2x^2 where x = -2 so i found out y = -7 so the coordiante are (-2,-7)

    I then diffrentiated to get -4x and found the gradient of the tanagnt whoch was 8. So the gradient of the normal will be - 1/8

    using Y=Mx+C i got y=-1/8 (-2) +C so c is equal to -27/4

    Y= 1/4x - 27/4

    So then i multiplied by 4 to get rid of the fractions giving

    4y=x-27 as the equation, but in the back of the book it says the answer is 8y-x-58 anyone see where i went worng? Thanks.
    • Thread Starter
    Offline

    0
    ReputationRep:
    Never mind i relasied after using the Y-y1=M(x-x1) formual how to do it .
    Offline

    3
    ReputationRep:
    (Original post by hazbaz)
    Find the equation of the normal to the curve at the point with the iven x coordinate.

    y= 1-2x^2 where x = -2 so i found out y = -7 so the coordiante are (-2,-7)

    I then diffrentiated to get -4x and found the gradient of the tanagnt whoch was 8. So the gradient of the normal will be - 1/8

    using Y=Mx+C i got y=-1/8 (-2) +C so c is equal to -27/4

    Y= 1/4x - 27/4

    So then i multiplied by 4 to get rid of the fractions giving

    4y=x-27 as the equation, but in the back of the book it says the answer is 8y-x-58 anyone see where i went worng? Thanks.
    You went wrong here:
    using Y=Mx+C i got y=-1/8 (-2) +C so c is equal to -27/4
    Substituting the (-2.-7) point into the equation of the line:
    -7=-1/8(-2)+C-> -29/4

    and here:
    Y= 1/4x - 27/4
    IN the equation of the normal line for tangent use the value of -1/8 calculated at the beginning
    y=-1/8x-29/4
    THe answer of the book is not correct in that form you wrote it,
    or there may be difference in the initial eqution of the curve or any data between you wrote here and given by the book.
 
 
 
Poll
Do you agree with the PM's proposal to cut tuition fees for some courses?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.