Not every triangle is a right-angle triangle, so we can't always use Pythagoras and SOHCAHTOA to find missing sides and missing angles. We instead use the sine rule or the cosine rule. They can both be used to find either missing sides or missing angles in any triangle (right angle or not). We label the sides as a, b and c, and angles as A, B and C.

We need to work out whether to use the sine rule or the cosine rule.

The sine rule is easier, so look for that one first. The sine rule is based on opposite pairs: you need an angle and the side opposite it, then you need either an angle and you want the opposite side OR you need a side and you want the opposite angle.

If we don't have the right combination of sides and angles for the sine rule, then we can use the cosine rule. For the cosine rule, we either want all three sides and to be looking for an angle, OR we need to have a side, angle and side all next to each other, and to then be wanting to find the third side.

SUBSCRIBE to the FuseSchool YouTube channel for many more educational videos. Our teachers and animators come together to make fun & easy-to-understand videos in Chemistry, Biology, Physics, Maths & ICT.

VISIT us at www.fuseschool.org, where all of our videos are carefully organised into topics and specific orders, and to see what else we have on offer. Comment, like and share with other learners. You can both ask and answer questions, and teachers will get back to you.

These videos can be used in a flipped classroom model or as a revision aid.

Find all of our Chemistry videos here:
https://www.youtube.com/watch?v=cRnpKjHpFyg&list=PLW0gavSzhMlReKGMVfUt6YuNQsO0bqSMV

Find all of our Biology videos here:
https://www.youtube.com/watch?v=tjkHzEVcyrE&list=PLW0gavSzhMlQYSpKryVcEr3ERup5SxHl0

Find all of our Maths videos here:
https://www.youtube.com/watch?v=hJq_cdz_L00&list=PLW0gavSzhMlTyWKCgW1616v3fIywogoZQ

Twitter: https://twitter.com/fuseSchool

Access a deeper Learning Experience in the FuseSchool platform and app: www.fuseschool.org
Follow us: http://www.youtube.com/fuseschool
Friend us: http://www.facebook.com/fuseschool

This Open Educational Resource is free of charge, under a Creative Commons License: Attribution-NonCommercial CC BY-NC ( View License Deed: http://creativecommons.org/licenses/by-nc/4.0/ ). You are allowed to download the video for nonprofit, educational use. If you would like to modify the video, please contact us: info@fuseschool.org