How do I know which trig formula to use in the exam?

When faced with a problem that involves triangles, there is a simple flowchart you can follow to determine which formula or identity you need to use! Firstly you must ask yourself whether the triangle has a right angle. If it has, you must then ask if it has any other angles (or you are asked to find another angle), if you are you can use the standard trig formula of SOHCAHTOA, if it hasn't, then you can use Pythagoras' theorem c2=a2+b2. However, if you haven't got a right angle, you must decide if your triangle has a side length you know the opposite angle to (some call this SSA), or if you have an angle in between two known sides (some call this SAS). If you know the opposite angle you use the Sine rule, if the angle is not opposite a known side you use the Cosine Rule. 

Joseph O. GCSE Maths tutor

2 years ago

Answered by Joseph, a GCSE Maths tutor with MyTutor

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


£24 /hr

Sioned D.

Degree: Law (Bachelors) - University College London University

Subjects offered:Maths, History+ 4 more

-Personal Statements-

“Hello! I'm a University College London Final year Law Student with a great deal of tutoring experience in English, Maths, Sciences and Entrance Exams. ”

Sahil M. A Level Biology tutor, GCSE Biology tutor, A Level Chemistry...
£20 /hr

Sahil M.

Degree: Medicine (Bachelors) - Manchester University

Subjects offered:Maths, Spanish+ 3 more

-Medical School Preparation-

“Hello! My name is Sahil and I am currently a medical student at the University of Manchester. I am really looking forward to tutoring you in Spanish, Chemistry, Biology or Maths as well as trying to help you during the difficult proce...”

PremiumRyan G. GCSE Maths tutor, GCSE Physics tutor, GCSE Computing tutor, A...
£22 /hr

Ryan G.

Degree: Electrical Engineering with Renewable Energy (Masters) - Edinburgh University

Subjects offered:Maths, Physics+ 2 more

-Personal Statements-

“ I will offer a wide range of ways to learn so you can find a way that best suits you!”

About the author

Joseph O.

Currently unavailable: for regular students

Degree: Law (Bachelors) - Liverpool University

Subjects offered:Maths


“I'm currently studying at the University of Liverpool, having started tutoring when in the sixth form and contining this into my undergraduate studies, volunteering in deprived schools for ActionTutoring. I am a very approachable and ...”

MyTutor guarantee

You may also like...

Other GCSE Maths questions

How can I know whether to multiply or add probabilities?

Eleri invests £3700 for 3 years at 2% per annum compound interest. Calculate the value of her investment at the end of the 3 years. Give your answer correct to the nearest penny.

Solve the simultaneous equations: 3x +4y = 18, and 5x - 2y = 4

Solve the simultaneous equation: 2x + y = 7 and 3x - y = 8

View GCSE Maths tutors

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