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	Math Help Forum > Pre-University Math Help > Pre-Algebra and Algebra equation of a graph User Name Save? Password Register Forum Rules FAQ Donate Members List Arcade Download MHF Flyer Search Today's Posts Mark Forums Read   Thread Tools Display Modes   #1   November 2nd, 2009, 12:07 PM GAdams Member   Join Date: Apr 2007 Posts: 161 Country: Thanks: 158 Thanked 2 Times in 2 Posts equation of a graph Bruce is given the graph of y = 3x - 2 He is going to draw a second graph on the same axes. He wants the x-coordinates of the points of intersection of the two graphs to be the solutions to the quadratic equation x^2 + x - 7 = 0 Work out the equation of the graph that needs to be drawn. Do not draw the graph. I have tried a few ways of doing this -not sure if I am right! Firstly: x^2 + x -7 = 3x - 2 and solved, but soon realised that this gave me the x-cocordinates but not the 'equation of the graph that needs to be drawn'. Secondly: adding the two equations and trying to solve as a pair of simultaneous equations -didn't get very far that way either. I'm a bit stumped, I'm not sure how I would go about tackling this kind of problem -help! __________________ This time next year, we'll be mathematicians. Advertisement     #2   November 2nd, 2009, 05:17 PM mr fantastic Flow Master   Join Date: Dec 2007 Location: Zeitgeist Posts: 12,243 Country: Thanks: 2,576 Thanked 4,763 Times in 4,195 Posts Quote: Originally Posted by GAdams Bruce is given the graph of y = 3x - 2 He is going to draw a second graph on the same axes. He wants the x-coordinates of the points of intersection of the two graphs to be the solutions to the quadratic equation x^2 + x - 7 = 0 Work out the equation of the graph that needs to be drawn. Do not draw the graph. I have tried a few ways of doing this -not sure if I am right! Firstly: x^2 + x -7 = 3x - 2 and solved, but soon realised that this gave me the x-cocordinates but not the 'equation of the graph that needs to be drawn'. Secondly: adding the two equations and trying to solve as a pair of simultaneous equations -didn't get very far that way either. I'm a bit stumped, I'm not sure how I would go about tackling this kind of problem -help! Let the required graph have the equation . The intersection of this graph with is found by solving . Re-arrange this so that you can compare it with . Hence get the values of a, b and c. __________________ There are two things you should never try to prove: the impossible and the obvious. The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low and achieving our mark. (Michelangelo Buonarroti) To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. The following users thank mr fantastic for this useful post: GAdams   #3   November 3rd, 2009, 11:18 AM GAdams Member   Join Date: Apr 2007 Posts: 161 Country: Thanks: 158 Thanked 2 Times in 2 Posts Quote: Originally Posted by mr fantastic Let the required graph have the equation . The intersection of this graph with is found by solving . Re-arrange this so that you can compare it with . Hence get the values of a, b and c. I'm not sure what you mean by 're-arrange this' , is it this?: ? I can't see how this would work. __________________ This time next year, we'll be mathematicians.   #4   November 3rd, 2009, 11:58 AM GAdams Member   Join Date: Apr 2007 Posts: 161 Country: Thanks: 158 Thanked 2 Times in 2 Posts ooh, ooh, I think I got it.... Is it: ?? __________________ This time next year, we'll be mathematicians.   #5   November 3rd, 2009, 11:46 PM mr fantastic Flow Master   Join Date: Dec 2007 Location: Zeitgeist Posts: 12,243 Country: Thanks: 2,576 Thanked 4,763 Times in 4,195 Posts Quote: Originally Posted by GAdams ooh, ooh, I think I got it.... Is it: ?? I get c = -9 .... __________________ There are two things you should never try to prove: the impossible and the obvious. The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low and achieving our mark. (Michelangelo Buonarroti) To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. The following users thank mr fantastic for this useful post: GAdams « functions help | Top | plus and minus logs » Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Trackbacks are Off Pingbacks are Off Refbacks are Off Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Pre-University Math Help     Pre-Algebra and Algebra     Geometry     Trigonometry     Pre-Calculus     Basic Statistics and Probability     Other topics University Math Help     Calculus     Analysis, Topology and Differential Geometry     Linear and Abstract Algebra     Number theory     Discrete Mathematics, Set Theory and Logic     Advanced Probability and Statistics     Advanced Applied Math     Differential Equations     Business Math     Other Advanced Topics Math Resources     LaTex Help     Mathematics Software Discussion     Calculator Discussion     Useful Math Websites     Mathematics News MHF Lounge     Chat Room         Live Chat     Problem of the Week     Pre-prints and other original work     Formal Debates         Proposals Challenges and Puzzles     Puzzles     Math Challenge Problems MHF Feedback and Announcements Forum     Question, Feedback and Comments     Announcements Our Other "Help Forums"     Physics Help Forum     Chemistry Help Forum All times are GMT -7. 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