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July 3rd, 2013, 12:23 AM   #1
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straight lines

Find the equation of straight lines which passes through the point (1,2) and makes an angle theta with the positive direction of the x-axis, where cos (theta) = -1/3.

Last edited by skipjack; September 4th, 2015 at 02:59 AM.
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July 3rd, 2013, 12:31 AM   #2
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Re: straight lines

What is the relationship between the angle of inclination and the slope of the line?
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September 4th, 2015, 02:58 AM   #3
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A =(theta)
Cos A = -1/3
Therefore Tan A = 8^(1/2)=m (slope of line )
(Y-2/x-1)=m=8^(1/2)



Hence, 2(2^(1/2))x - y - 2(2^(1/2)) + 2 =0
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September 4th, 2015, 03:03 AM   #4
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As the question doesn't say otherwise, tan(θ) can be positive or negative.
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September 4th, 2015, 06:29 AM   #5
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Quote:
Originally Posted by skipjack View Post
As the question doesn't say otherwise, tan(θ) can be positive or negative.



The slope ranges from [0 ,pi )
Now as cos theta is -ve it lies from ( 90° , 180°)
Therefore tan theta is also -ve
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September 4th, 2015, 06:35 AM   #6
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Quote:
Originally Posted by Yash Malik View Post
A =(theta)
Cos A = -1/3
Therefore Tan A = 8^(1/2)=m (slope of line )
(Y-2/x-1)=m=8^(1/2)



Hence, 2(2^(1/2))x - y - 2(2^(1/2)) + 2 =0
Sorry
Tan theta is -ve
So eqn shd be
2(2^(1/2))x + y - 2(2^(1/2)) - 2 =0

Btw thnx fr reminding me
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