I am currently stuck on a particular question in maths that has completely thrown me.

I have been given:

Va = 2sin (314.2t)

Vb = 2sin (314.2t-70°)

The task is to determine a single wave from a combination (additive) of 2 waves.

I have completed the graph and written down the formula for the resulting wave;

Vc = 3.26sin (314.2t+36°)

This may not be correct but it must be in the form Vsin (wt-phi)

I am then asked to use trigonometry to derive an expression for the resultant wave form in the same form?

This has completely wiped me, the first thing that comes to mind is sina+b=sinacosb+cosasinb but have no idea if I am thinking along the right lines or what to do with it if I am!!

Please help!!

Sian.