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March 27th, 2014, 04:41 AM  #1 
Newbie Joined: Mar 2014 Posts: 6 Thanks: 0  find the equations
Hello, hopefully I'm on the right bit I need to find the equations of a few plots first is: A(1,4) B(52) I'd like to know if this is the correct way: m= 24/51 = 6/4 =3/2 so m= 3/2 4=3/2x + c c=11/2 so the equation is y=3/2x11/2 
March 27th, 2014, 04:56 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 21,036 Thanks: 2274 
Take care to include all the necessary symbols. For example, did you mean "B(52)" to be "B(5,2)" or "B(5,2)"?

March 27th, 2014, 05:00 AM  #3 
Newbie Joined: Mar 2014 Posts: 6 Thanks: 0  Re: find the equations
ah sorry mean B(5,2)

March 27th, 2014, 05:27 AM  #4  
Math Team Joined: Sep 2007 Posts: 2,409 Thanks: 6  Re: find the equations Quote:
or That is what you are trying to do but you are being careless with signs! I presume the "4" is from (1, 4) so x should be 1: 4= (1/3)(1)+ c so c= 4+ 1/3= 12/3+ 1/3= 11/3 Quote:
Another way of doing this whole problem is to recognize that any (nonvertical) line can be written as y= mx+ c for some numbers m and c. Since the point (1, 4) is on the line, 4= m(1)+ c. Since (5, 2) is on the line, 2= m(5)+ c. Eliminate c from the equations by subtracting the first equation from the second: (2 (4))= 5m+ c (m+ c) or (2+ 4)= 2= 6m so m= 2/6= 1/3. You should see that the calculations there are exactly the same as before. Since m= 1/3, 2= (1/3)(5)+ c so c= 2 5/3= 6/2 5/3= 11/3 OR 4= (1/3)(1)+ c so c= 4+ 1/3= 12/3+ 1/3= 11/3. In either case, y= (1/3)x 11/3 again.  
March 27th, 2014, 05:36 AM  #5 
Newbie Joined: Mar 2014 Posts: 6 Thanks: 0  Re: find the equations
Explains a lot, thanks. Going to have another shot at it with your help, and see if I can get it correct this time before moving on.

March 27th, 2014, 07:27 AM  #6 
Newbie Joined: Mar 2014 Posts: 6 Thanks: 0  Re: find the equations
ok next one P(1,3) Q(4,2) = = m= 3= (x)+c 3+() = so the equation should be y=x+ 
March 27th, 2014, 08:20 AM  #7 
Newbie Joined: Mar 2014 Posts: 6 Thanks: 0  Re: find the equations
edit i mean not 2/3 
March 27th, 2014, 11:21 AM  #8  
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,597 Thanks: 1039  Re: find the equations Quote:
y = mx + b [1] m = (2  3) / (4  1) = 1/3 Substitute in [1]: y = (1/3)x + b [2] Using P(1,3) and substituting x=1 and y=3 in [2]: 3 = (1/3)(1) + b 3 = 1/3 + b b = 3 + 1/3 b = 9/3 + 1/3 b = 10/3 Substitute in [2]: y = (1/3)x + 10/3 You don't need to do it EXACTLY that way...but why take a chance...get my drift?  
March 27th, 2014, 11:33 AM  #9 
Newbie Joined: Mar 2014 Posts: 6 Thanks: 0  Re: find the equations
ok thanks Denis practise practise!!!!


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