So right now this information seems kind of useless but if we could put this somehow in terms of B then we'll have will will be making progress as we know information about angle B so let's see what we can do so the first thing i would use is well sine of 2A - let me just rewrite each of these so sine of i just say sine of two times anything that's just the same thing as and this is called the double angle formula so this is i might be wrong i was for the actual names of them but sine of two time something is two sine of that something times the cosine of that times the cosine of that something and you'll see that in any trigonometric book on the inside cover even a lot of calculus books
จะไม่มีค่า แต่หากเราทําได้ ใส่มันลงไปในรูปของ B