There are three different formulae for the equation of a line
y= mx + x
y  y1 = m(x  x1)
ax + by + c = 0
Which one is easier and works all the time.

Sarah2014
my teacher says you need to learn all three i get so mixed up on these too!!

hamzamughees
Which one do you think is easiest though?

Sarah2014
it depends on the question given but in my opinion i find ax+by+c=0 easy

hamzamughees
Thanx

Sarah2014
youre welcome

Chris241197
i've never learnt ax+by+c =0 and still got A in jc maths, and the fist and second formulae are just variations on each other so you only need to learn the yy1=m(xx1), however ironically you don't need to learn any of these as they are in the formula book.

Sarah2014
but how would you know which one to use then? @chris241197

1357
it says in the formula book what you use them for

Sarah2014
ok thanks

hamzamughees
When I learned these formulae my teacher said that each of these equations are better in some occasions.

Sarah2014
im so confused like how do you know when reading a question which formula you use?

hamzamughees
exactly

Sarah2014
ughhh so confusing haha

Roberto Mane
It usually tells you in the question,like in an area and volume question where it tells you to express your answer in terms of pi.

Sarah2014
oh ok thanks

themathstutor.ie
y= mx + x
should be
y= mx + c
Eamonn  TheMathsTutor.ie

hamzamughees
Oh yea I noticed that later

hamzamughees
Sorry my bad and thanx

bridgetown1
y=mx+c gives you the slope (m, rises/run) and the y intercept.
this equation is easiest to work with, makes graphing easier and can be worked out from a well drawn graph.

themathstutor.ie
y  y1 = m(x  x1)
is used if you have the slope of the line and the coordinates of a point on the line. If you know these, you can sub them in to find out the equation of the line.
And if you don't know the slope, but have 2 points, then there is a formula to find the slope of the line between those points, so do that first, then use the above formula to find the equation of the line.
Eamonn  TheMathsTutor.ie

themathstutor.ie
As for
ax + by + c = 0
This form is not as easy to interpret as y = mx + c
You could extract some info about the slope and the y intercept e.g. the slope would be a/b, and the y intercept is c/b in this case.
But you might find it easier to rearrange whatever equation you are given, so as to put it in the form y=mx+c. In doing so, you need to be careful to change the sign of any term you bring across the = sign, and also if you divide one term, you must divide them all by the same.
Once in the form y = mx + c, it's easy to interpret.
Eamonn  TheMathsTutor.ie

hamzamughees
thank you so much guys.

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