Turn on thread page Beta
    • Thread Starter
    Offline

    11
    ReputationRep:
    Hi,

    Please could I have some help on this question.

    Q1. a) The tangent drawn to the curve  y = 2x^2 + 3x at the point P (x, y) is parallel to the x-axis.
    Determine the coordinates of P.

    b) The line  y = 2x - 4 is a tangent to the curve  y = x^2 - 2x at the point P (x, y). What are the coordinates of P?

    I did the questions before that asked me to find the gradient/equation of the tangent and normal to curve, but don't understand this question, particularly the bit about coordinates and parallel to x-axis?

    Thanks.
    Offline

    9
    ReputationRep:
    Q1. a) parallel to the x achsis means that the gradient is 0 ... so differentiate it and solve for x

    b) you are given the equation of the line... y=mx+b where m is the gradient... if you differentiate the curve and let it equal to the gradient you can find then the x coordinate of P with that coordinate you can easily find the Y coordinate by simply plugging it into one of those equations
    • Thread Starter
    Offline

    11
    ReputationRep:
    (Original post by darkness9999)
    Q1. a) parallel to the x achsis means that the gradient is 0 ... so differentiate it and solve for x

    b) you are given the equation of the line... y=mx+b where m is the gradient... if you differentiate the curve and let it equal to the gradient you can find then the x coordinate of P with that coordinate you can easily find the Y coordinate by simply plugging it into one of those equations
    Thanks for the quick reply. On a I got x as - 3/4 which is right according to the book, and I thought y = 2  -\frac{3}{4}^2 + (3 x -\frac{3}{4})

    but according to the book it is y = 2  -\frac{3}{4}^2 , and therefore y = -9/8 . I don't understand why the + 3 x -\frac{3}{4} is ignored..

    Can you explain please?

    Thanks
    Offline

    9
    ReputationRep:
    (Original post by Darkest Knight)
    Thanks for the quick reply. On a I got x as - 3/4 which is right according to the book, and I thought y = 2  -\frac{3}{4}^2 + (3 x -\frac{3}{4})

    but according to the book it is y = 2  -\frac{3}{4}^2 , and therefore y = -9/8 . I don't understand why the + 3 x -\frac{3}{4} is ignored..

    Can you explain please?

    Thanks

    ok... in this question u already calculated the x value..which is right... then to get the Y value u just put the x value in the function... so y=2x^2 + 3x.... if u substitude x in there u will get - 9/8
 
 
 
Poll
Should predicted grades be removed from the uni application process
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.