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 July 3rd, 2013, 12:23 AM #1 Newbie   Joined: Jul 2013 Posts: 1 Thanks: 0 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. July 3rd, 2013, 12:31 AM #2 Senior Member   Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 521 Math Focus: Calculus/ODEs Re: straight lines What is the relationship between the angle of inclination and the slope of the line? September 4th, 2015, 02:58 AM #3 Senior Member   Joined: Sep 2015 From: 4th Dimension Posts: 146 Thanks: 13 Math Focus: Everything (a little bit) 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 September 4th, 2015, 03:03 AM #4 Global Moderator   Joined: Dec 2006 Posts: 20,927 Thanks: 2205 As the question doesn't say otherwise, tan(θ) can be positive or negative. September 4th, 2015, 06:29 AM   #5
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Quote:
 Originally Posted by skipjack 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    September 4th, 2015, 06:35 AM   #6
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Math Focus: Everything (a little bit) Quote:
 Originally Posted by Yash Malik 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 Tags lines, straight Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post devvaibhav Algebra 11 June 2nd, 2013 12:47 PM alloy Algebra 1 November 3rd, 2012 02:27 AM alloy Algebra 1 October 30th, 2012 08:56 AM mikeportnoy Algebra 13 December 22nd, 2009 12:45 PM Apprentice123 Algebra 0 June 20th, 2008 05:08 AM

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