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GCSE Unit Two Maths: Perpendicular & parallel lines in y=mx+c graphs

Hi - need some urgent help with y=mx+c perpendicular. Can anyone explain it to me please?

Need it for my Unit Two resit - thanksssss :biggrin:
Reply 1
Original post by taamuuu
Hi - need some urgent help with y=mx+c perpendicular. Can anyone explain it to me please?

Need it for my Unit Two resit - thanksssss :biggrin:


parallel lines will be y = mx + anything

perpendicular will be y = (-1/m)x + anything
Reply 2
If two lines are perpendicular then the product of their gradients is -1
Reply 3
To reiterate what everyone else is saying:

Let the first line be y=m1x+c1y=m_1x+c_1

Let the second line be y=m2x+c2y=m_2x+c_2




If

m2=m1m_2=m_1

the lines are parallel.




If

m1m2=1m_1m_2=-1

or

m2=1m1m_2=\dfrac{-1}{m_1}

the lines are perpendicular.
(edited 11 years ago)

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