Im not clear if we can use 0 as Y intercept to find out X

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[email protected]: Master | Next Rank: 500 Posts; Posts: 429; Joined: Wed Sep 19, 2012 11:38 pmFollowed by: 4 members; Thanked: 6 times

by [email protected] » Thu Aug 01, 2013 4:56 am

A line has a slope 3/4 and intersects the points (-12, -39).At which point does the line intersect the x axis.

My question is what are the questions in which we consider Y intercept to be 0 to find X and vice versa.

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Source: Beat The GMAT — Problem Solving | Thu Aug 01, 2013 4:56 am

snigdha1605: Senior | Next Rank: 100 Posts; Posts: 43; Joined: Fri Feb 22, 2013 10:41 pm; Thanked: 3 times

by snigdha1605 » Thu Aug 01, 2013 5:23 am

Hi,

In the below question

At which point does the line intersect the x axis.

we would take Y = 0 ( when a line intersects the x axis, its Y coordinate would be 0. whereas the x Coordinate would have a definite value)

Question -

A line has a slope 3/4 and intersects the points (-12, -39).At which point does the line intersect the x axis.

Slope line eq -
y= mx + c ( m slope , c is intercept on y axis when x= 0)

Plug the values of x, y, m to find c

-39 = 3/4 * (-12) + c
c= -30

now , To find the point where the line intersects at x axis , substitute y=0 in the above eq

0=mx +c
x= -c/m = 30/ (3/4) = 40

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nipunranjan: Senior | Next Rank: 100 Posts; Posts: 37; Joined: Wed Mar 10, 2010 3:35 am; Thanked: 4 times; GMAT Score:700

by nipunranjan » Thu Aug 01, 2013 10:50 am

See X-axis means Y=0
Y-axis means X=0

So for X intercept you should take Y=0.

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