Lösung 4.3:7a
Aus Online Mathematik Brückenkurs 1
We can write the expression \displaystyle \sin (x+y) in terms of \displaystyle \sin x, \displaystyle \cos x, \displaystyle \sin y and \displaystyle \cos y if we use the addition formula for sine,
In turn, it is possible to express the factors \displaystyle \cos x and \displaystyle \cos y in terms of \displaystyle \sin x and \displaystyle \sin y by using the Pythagorean identity,
Because x and y are angles in the first quadrant, \displaystyle \cos x and \displaystyle \cos y are positive, so we in fact have
Finally, we obtain
