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

    0
    ReputationRep:
    Hello, my friend and I are completely stuck on part c of this vectors question.
    "The straight line L1 and L2 have the vector equations r=(i+4j+2k)+t(8i+5j+k) and r= (I+4j+2k) +s(3i+j) respectively, and P is the point with the coordinates (1,4,2).
    a) Show that the point Q lies on L1
    b) Find the cosine of the acute angle between L1 and L1 [My friend and I both got 29/30 as the cosine of the acute angle]
    c) Find the possible coordinates of the point R, such that R lies on L2 and PQ=PR"

    We are very confused on this matter and can't find any questions/answers similar in order to try and work out how to solve this question. If anyone is able to help it would be very greatly appreciated.

    Thank you very much.
    Offline

    15
    ReputationRep:
    What are the coordinates of Q?
    • Thread Starter
    Offline

    0
    ReputationRep:
    (9,9,3)
    Offline

    15
    ReputationRep:
    Have you drew a diagram? Please post your workings or answers if you can.
    • Thread Starter
    Offline

    0
    ReputationRep:
    For part c?
    Offline

    1
    ReputationRep:
    As B said, drawing a diagram does help with stuff like this, even if it looks a bit weird in 3D coordinates.

    If you figure out the distance PQ = Q - P, then R - P should give you the same value.

    The 2 things you will need here is the formula for the distance between 2 points and the general equation for a point on the line L2. You know R = [r1,r2,r3] = [1,4,2] + s[3,1,0] so you only really need to figure out what s could be to get the answers.
    • Thread Starter
    Offline

    0
    ReputationRep:
    Okay, thank you, I have got the answers to be (10,7,2) and (-8,1,2).
    Offline

    1
    ReputationRep:
    No problem, I get the same
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Brexit voters: Do you stand by your vote?
    Help with your A-levels

    All the essentials

    The adventure begins mug

    Student life: what to expect

    What it's really like going to uni

    Rosette

    Essay expert

    Learn to write like a pro with our ultimate essay guide.

    Uni match

    Uni match

    Our tool will help you find the perfect course for you

    Study planner

    Create a study plan

    Get your head around what you need to do and when with the study planner tool.

    Study planner

    Resources by subject

    Everything from mind maps to class notes.

    Hands typing

    Degrees without fees

    Discover more about degree-level apprenticeships.

    A student doing homework

    Study tips from A* students

    Students who got top grades in their A-levels share their secrets

    Study help links and info

    Can you help? Study help unanswered threadsRules and posting guidelines

    Sponsored content:

    HEAR

    HEAR

    Find out how a Higher Education Achievement Report can help you prove your achievements.

    Groups associated with this forum:

    View associated groups
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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.