Hello S2KrazyWhat you need to know:

- Double-angle formulae. These are the ones you need here:

and

- When the various trig functions are positive. Here's the diagram:

(Remember ACTS starting in QI and going clockwise.)

- and

So for #3, A is in QIII, so only tangent is positive: sine and cosine are both negative. So if (Pythagoras) and .

Using :For # 4, x is in QIV, so only cosine is positive; sine and tangent are negative. So (Pythagoras)

(You can check this out.)For #5, all functions are positive in QI. So (Pythagoras)

(Check my working)Grandad