How can I tell if two lines are perpendicular from the equations?

In order to compare two equations they need to be in the same form. This means that the y's have to be on the left, and the x's have to be on the right - so the first step is to rearrange both of the equations that you are comparing to be in this form: y = mx + c where m is a number, and c is a number.

When we are talking about perpendicular lines, we really don't care about the c value as all this does is move the lines upwards and downwards along the y axis - what is important is m, the gradient value. Because we have two equations, we have two values of m to look at: m1, and m2. If the lines are perpendicular, then m1 will be the negative reciprocal of m2 - what does that mean?! Simply, that m1 = -1/m2. - Or even more simply, that if we multiply m1 by m2, the answer will be -1. 

In summary: rearrange, and then multiply the m values to check if the answer is -1.

Ben S. GCSE Maths tutor, GCSE Science tutor, GCSE Physics tutor

1 year ago

Answered by Ben, who has applied to tutor GCSE Maths with MyTutor

Still stuck? Get one-to-one help from a personally interviewed subject specialist


£18 /hr

Melissa P.

Degree: Mathematics (Bachelors) - Birmingham University

Subjects offered: Maths, Spanish


“About me:  I am currently studying for a Maths degree at the University of Birmingham. I have enjoyed Maths since I was very young and hope I can pass some of this on to you!  I am very friendly. I have been coaching gymnastics since...”

£18 /hr

Harry M.

Degree: Physics (Masters) - Exeter University

Subjects offered: Maths, Physics


“Hey everyone,If you're reading this, then I assume you're stuck on something physics-y or maths-y. If so, thenI can help! I'm a Physics student at Exeter University and I can be your guru. Physics reduces the complex world to somethi...”

£18 /hr

Madeleine P.

Degree: Economics (Bachelors) - Durham University

Subjects offered: Maths, -Personal Statements-

-Personal Statements-

“About me I am reading Economics at Durham University. I have always had a passion and love for Mathematics and really enjoy now using it at degree level when tackling real world problems. I am very patient and freindly and have a desi...”

About the author

£18 /hr

Ben S.

Degree: Mechatronic Engineering (Masters) - Manchester University

Subjects offered: Maths, Science+ 1 more



MyTutor guarantee

You may also like...

Other GCSE Maths questions

Find the highest common factor (HCF) of 12 and 18.

Lisa, Max and Punita share £240 in the ratio 3 : 4 : 8 How much more money than Lisa does Punita get?

Write 825 as a product of its prime factors.

Rearranging formulae

View GCSE Maths tutors


We use cookies to improve our service. By continuing to use this website, we'll assume that you're OK with this. Dismiss