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What is the equation of the line that passes thru (1,1) and

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What is the equation of the line that passes thru (1,1) and [#permalink]

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20 Feb 2006, 18:31
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What is the equation of the line that passes thru (1,1) and (-4,-2).

find the y-intercept also.
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20 Feb 2006, 18:35
What is the equation of the line that passes thru (1,1) and (-4,-2).

find the y-intercept also.

m= -2-1 / (-4-1) = -3/-5 = 3/5

equation of line = y = 3/5 x + b => b = 2/5

equation o fline y = 3/5 x + 2/5
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20 Feb 2006, 18:38
how did you get the y-intercept? Its been so long
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20 Feb 2006, 18:44
y-intercept -> where the line intersects the y-axis.

Start with the equation of the line, but let y = 0.

y = 3/5 x + 2/5
0 = 3/5 x + 2/5
0 = 3x + 2
-2 = 3x
x = -2/3

(x, y) = (-2/3, 0)
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20 Feb 2006, 18:45
y-intercept is the value of b.

I think what zoelef has is the x-intercept.
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20 Feb 2006, 18:50
Avis u r right for y intercept put x = 0 in the equation u got ... so in the equation given by y = 3/5 x + 2/5 putting x =0 u get y = 2/5

so at the point (0,2/5 ) the line will cut the y axis .
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20 Feb 2006, 18:57
Avis wrote:
y-intercept is the value of b.

I think what zoelef has is the x-intercept.

As a mathematics major, me fungling something that basic is solid proof that college makes you stupider.
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21 Feb 2006, 08:08
Avis wrote:
y-intercept is the value of b.

I think what zoelef has is the x-intercept.

but how u got b ==> 2/5 ?? i dont understand...
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21 Feb 2006, 08:21
I could not understand how you got the value of b.

Way2go
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21 Feb 2006, 08:32
razrulz wrote:
Avis wrote:
y-intercept is the value of b.

I think what zoelef has is the x-intercept.

but how u got b ==> 2/5 ?? i dont understand...

You must know the formula in such cases...

We have (1;1) (-4;-2) on the coordinate plane...

the basic equation here is y=mx+b (where m is the slope of the line, x is the x intercept of the line and b is y intercept of the line)

Now first of all we need a slope of the line:
The slope of the line is m=change in y/change in x or (y1-y2)/(x1-x2)
Plug in the numbers... m=(-2-1)/(-4-1)=3/5

Now to find the equation use the same formula which we used in order to find the slope....

m=(y1-y)/(x1-x)....... m(x1-x)=y1-y once again plug in the values for x1 and y1 and m....

3/5(-4-x)=-2-y
-12/5-3/5x=-2-y
-y=2-12/5-3/5x..... 2-12/5 equals -2/5
-y=-2/5-3/5x
y=3/5x+2/5
now we remember the formula y=mx+b where b denotes y intercept, this means y intercept is 2/5.....

If we were also asked to calculate the x intercept we would give y the value of 0 and solve the equation....
3/5x+2/5=0
3/5x=-2/5
x=-2/3, this line croses x axis at -2/3.....
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21 Feb 2006, 17:07
thanks guys, much appreciated
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