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August 9th, 2008, 09:21 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, 10:24 AM  #2  
Senior Member Joined: Jul 2008 Posts: 895 Thanks: 0  Re: straight line Q Quote:
The text must contain some information. If you rearrange the equation ax + by = 4 to "slopeintercept 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, 10:29 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] 

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