My Math Forum straight line Q

 Algebra Pre-Algebra and Basic Algebra Math Forum

 August 9th, 2008, 08:21 AM #1 Member   Joined: Aug 2007 Posts: 39 Thanks: 0 straight line Q the point (2,3) lies on the line ax + by = 4 which has a gradient of 2. find the values of the constants a and b and hence, in its general form, the equation of the straight line. i know the equation of the straight line is y = 2x - 1, and in its general form [ax + by + c = 0] is 2x - y - 1 = 0. but i don't quite get how to work out the constants. could someone explain this please also because its not explained in my textbook thanks!
August 9th, 2008, 09:24 AM   #2
Senior Member

Joined: Jul 2008

Posts: 895
Thanks: 0

Re: straight line Q

Quote:
 i know the equation of the straight line is y = 2x - 1.... but i don't quite get how to work out the constants.
How did you then find that the equation is y=2x-1 without first finding the values of constants ...which is really the essence of the problem. Can you show what you have done so far?

The text must contain some information. If you re-arrange the equation ax + by = 4 to "slope-intercept form", what do you get? If you substitute the point (2,3) into the equation what do you get? Both of these will give you two equations in a and b. Solve them for the solution.

 August 9th, 2008, 09:29 AM #3 Member   Joined: Aug 2007 Posts: 39 Thanks: 0 Re: straight line Q sorry, i didn't work it out, should've mentioned this is the answer from the back of the book. the equation is 2x - y = 1 or y = 2x - 1 [when rearranged]

 Tags line, straight

### math forum straight line

Click on a term to search for related topics.
 Thread Tools Display Modes Linear Mode

 Similar Threads Thread Thread Starter Forum Replies Last Post Chikis Physics 10 September 8th, 2012 04:53 PM shalikadm Algebra 3 January 24th, 2012 10:48 PM poochie03 Algebra 3 November 5th, 2011 12:00 PM outsos Algebra 7 December 23rd, 2010 07:15 PM Kiranpreet Algebra 3 August 10th, 2008 07:45 AM

 Contact - Home - Forums - Cryptocurrency Forum - Top