#help

[gloomy bronze]

Why is sin 2a = 2 cos a sin a

[sinful storm]

sin(a + b) = sin(a) cos(b) + cos(a) sin(b)
sin(2a)
= sin(a + a)
= sin(a) cos(a) + cos(a) sin(a)
= sin(a) cos(a) + sin(a) cos(a)
= 2 sin(a) cos(a)

[old fractal]

Because it is that is just simple maths noob

[gloomy bronze]

I know this but
Why is sin a cos b + cos a sin b = sin (a+b)

[gloomy bronze]

How old are you?

[sinful storm]

I can provide a visual prove, and it also proves cos(a+b)

[elfin scroll]

the area of triangle OPQ, denoted by S, is given by$ 1/2 \cdot 1 \cdot 1 \cdot \sin (a+b) $ which is a fact of elementary geometry. Furthermore, S can be expressed as $1/2\cdot (sin(a)cos(b)+cos(a)sin(b))$ using the Sarrus formula which is a fact from coordinate geometry.

[trail zephyr]

c０009

[unique finch]

You could actually show sin(a+b) = sinacosb + cosasinb instead of showing that they both produce same results of some quantity.

[gloomy bronze]

Yes pleade

[gloomy bronze]

What?

Its hard to understand