A-Level Maths: E6-06 Compound Angles: Using Double Angle Formulae to Solve Equations

[baldjacob]

you're the only reason I am surviving A-level maths, thanks

[sughrashabir]

Can you please make another video with more examples of double angle formulae. Harder questions.
Cos3xcosx=sin3xsinx
Or neglected tan equations

[JK-vmyo]

For 2, Im not sure how cos2x is seen as 2y when it should be y no? And in that case it cant be factorised. I see how it would be seen as equivelent to 2y if it was 2cos2x? Im cnfused sir?

[justme]

For the first question you said I cannot divide by sinx, because I will lose solutions.
Why would you lose solutions?
And if I get a similar question, how would I recognise that I will lose solutions by dividing?

[cbb]

Why would you add the period to the x value at the end?

[JK-vmyo]

Is it valid to do Sin4x=(2x+2x) thenn use the formula and then we can just sub the x with 2x, it gives same result. I just need a bit of a more logical way of doing it rather than pulling out of nowhere, could u let me know if this is valid tho sir, thanks

[MathBuz]

Jack can we write like this:
For interval 0 <= x < 2 pi
You can write interval for 2x by multiplying inequality by 2 i.e. 0 <= 2x < 4 Pi
according to this interval we can clearly see that 2 pi is included.
But finally we need to find for the value of x, so even if we use just 0 is fine, but ignoring 2x = 2 Pi is logically not sound i think...

[amirah]

I don't really understand why you would add the period at the end. I know that it gives you the second solution but how do I know to do that in a test or exam?

[singularityhq]

I'm having difficulty displaying this on Desmos. Do you have any examples?

[subzerovsscorpion]

sir, just lil confusing.Q2 : why you didn't change the cos2x too?