Differentiating trig by first principles

Because that's another standard A level result that is proved earlier in B&C

I haven't got time to find / scan the original but this is something even simpler that just relies on taking a sector of a circle with central angle x, drawing a chord and a tangent and working out lower and upper bounds for the sector area, then dividing through by sin x and considering what happens as x gets close to 0 (radians).

I have to say, both this and the sin x derivative proof are things that I thought all standard A level books still covered, but maybe this is no longer the case

I know the one, though I can't say I remember learning it at A-level the squeeze theorem (though intuitive) wasn't a result that was covered.
I might be mistaken, I remember the horrible geometric proof for sines of sums and the like, maybe it was mixed in with those.

I know the one, though I can't say I remember learning it at A-level the squeeze theorem (though intuitive) wasn't a result that was covered.
I might be mistaken, I remember the horrible geometric proof for sines of sums and the like, maybe it was mixed in with those.

I know the one, though I can't say I remember learning it at A-level the squeeze theorem (though intuitive) wasn't a result that was covered.
I might be mistaken, I remember the horrible geometric proof for sines of sums and the like, maybe it was mixed in with those.