The Sum and Difference Formulas - derivations (3 of 4: Trigonometric Identities) (A level)

In this video I derive the sum and difference formulas and give some explanation as to how and why they are used.

Also I forgot to mention another useful application of these formulas is modelling. It is often useful to convert a function in the form of e.g. sinAcosB + cosAsinB into the form sin(A+B) which makes it easier to work with in some situations.

[electrik_loss]

Heya, at 2:43, you could explain how you got √2 (√3+1)/4? I'm kinda confused.

[giack]

Hello! Thank you for your very clear explanation, i have a question: this proofs seem true only when alfa and beta are acute angles. How to prove that they hold for any alpha and beta (even negative or 188 degrees or 520 degree or any other angle)?

[Kinggballer]

Hey, At the 16:56 mark, you solved that angle and said it is A, how is that possible? Also, I solved it to be A+B

[lifeishappening]

I know that you have to know exact trig values for GCSE but do you need to Know this as well ?

[jamestanny]

What if you got tan(2x - 84deg)=0? Nobody even teaches stuff like this...

[aLittlePal]

it is a decently logical challenging subject, trig, but the more you get into it, it changes into an academical damping machine

how about some trig function of 16.4976
so you can see these tricks are boring meaningless stuff, plays with easy radian degree of 35, 45, 60, etc

human build calculator for this, you are not studying for becoming a human calculator