# C1: Straight Lines FormWatch

Thread starter 12 years ago
#1
Hi :

sometimes they say put your answer in the form ay + bx + c = 0 , where a and b are integers
is it okay if work the equation out using y = mx + c then change it to that form in the last line of working?

secondly i was doing some past papers for c1 and sometimes when they dont ask you what form to give the equation of the line or tangent in, i put down y = mx + c form, and its not on the mark scheme, will i be penalised?

thirdly some1 please teach me the other way so i stop asking these bliiming stupid questions

thanks
0
12 years ago
#2
(1) that's okay
(2) you won't be penalised
(3) tbh I always work out y=mx+c or y-y1=m(x-x1)
The ax+by+c=0 is only useful when you want integral constants as everything can be scaled as required. Also, it's useful when working with circles etc.
0
12 years ago
#3
(Original post by footballhead)
sometimes they say put your answer in the form ay + bx + c = 0 , where a and b are integers
is it okay if work the equation out using y = mx + c then change it to that form in the last line of working?

thirdly some1 please teach me the other way so i stop asking these bliiming stupid questions
If you have
y = mx + c, then only if m or c is a fraction, you need to change it in the form ay + bx + c = 0, by multiplying everything by denominator of fraction and taking everything to one side.
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