Join TSR now and get all your revision questions answeredSign up now

Equation of a parallel line (help)

    • Thread Starter
    Offline

    3
    ReputationRep:
    Q) write the equation of a line that is parallel to the line 2x - 4y = 8 and goes through the point (3,0)

    I rearranged in the form y=mx + c and got y= 1/2x - 2

    Then I work out the equation of the parallel line by doing this right? y-y1 = 1/2 (x-x1)

    so its y-0 = 1/2 (x-3)

    and I got y= 2x - 3

    and its wrong
    Offline

    3
    ReputationRep:
    (Original post by samantham999)
    Q) write the equation of a line that is parallel to the line 2x - 4y = 8 and goes through the point (3,0)

    I rearranged in the form y=mx + c and got y= 1/2x - 2

    Then I work out the equation of the parallel line by doing this right? y-y1 = 1/2 (x-x1)

    so its y-0 = 1/2 (x-3)

    and I got y= 2x - 3

    and its wrong
    It was all perfect until the very last bit! y = 1/2 ( x - 3 ) becomes:y = x/2 - 3/2
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by wightsnowolf)
    It was all perfect until the very last bit! y = 1/2 ( x - 3 ) becomes:y = x/2 - 3/2
    don't we x by 2 and expand the bracket?
    Offline

    3
    ReputationRep:
    (Original post by samantham999)
    don't we x by 2 and expand the bracket?
    That was the expansion of the bracket. The 1/2 got multiplied by all elements inside the bracket
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by wightsnowolf)
    That was the expansion of the bracket. The 1/2 got multiplied by all elements inside the bracket
    so did you get the answer by x outside number by inside numbers? 1/2(x-3)

    1/2x - 3/2 ?
    Offline

    2
    ReputationRep:
    (Original post by samantham999)
    don't we x by 2 and expand the bracket?
    It's the same thing but it can just make it easier in some cases by allowing you to work with whole numbers rather than fractions. If you did multiply by 2 the answer should be 2y=x-3.
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by Samii123)
    It's the same thing but it can just make it easier in some cases by allowing you to work with whole numbers rather than fractions. If you did multiply by 2 the answer should be 2y=x-3.
    wouldn't i multiply the whole equation not just 2y?
    Offline

    2
    ReputationRep:
    (Original post by samantham999)
    wouldn't i multiply the whole equation not just 2y?
    That's what I meant. If you double y-0=1/2(x-3) it comes out to 2y=1(x-3) and obviously you don't need to expand it so it just becomes 2y=x-3.
    • Thread Starter
    Offline

    3
    ReputationRep:
    for this question why did we x by 3 then?

    find the equation of a line parallel to the line 3y-2x-6=0 and passing through the point (-1,-2)
    y=2/3x + 2

    then we use y-y1 = mx (x-x1)

    y--2 = 2/3 (x--1)

    and then we X by 3

    we get: 3y + 6 = 2x + 2

    then divide by 3 and -6

    and we get y= 2/3x - 4/3
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by Samii123)
    That's what I meant. If you double y-0=1/2(x-3) it comes out to 2y=1(x-3) and obviously you don't need to expand it so it just becomes 2y=x-3.
    I get it so we can do it either way, I just made the mistake by x 2 by x when it was 1/2
    Offline

    2
    ReputationRep:
    (Original post by samantham999)
    I get it so we can do it either way, I just made the mistake by x 2 by x when it was 1/2
    Yh sometimes the question will ask for integers so you can't always leave it as a fraction.
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by Samii123)
    Yh sometimes the question will ask for integers so you can't always leave it as a fraction.
    we just divide so we get rid of the fraction?
    Offline

    2
    ReputationRep:
    (Original post by samantham999)
    we just divide so we get rid of the fraction?
    X the whole equation by the denominator so when you had the one with 1/2x you x it all by 2.
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by Samii123)
    X the whole equation by the denominator so when you had the one with 1/2x you x it all by 2.
    ah I keep saying divide!!! I meant x the equation to get rid of the fraction (i.e the opposite )
    thanks
 
 
 
Poll
Which party will you be voting for in the General Election 2017?
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

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