[Pre-Calc] Please Help! I don’t know where to start. How do I do this?

See Below.

Step-by-step explanation:

Problem A)

We have:

When in doubt, convert all reciprocal trig functions and tangent into terms of sine and cosine.

So, let cscθ = 1/sinθ and tanθ = sinθ/cosθ. Hence:

Cancel:

Let 1/cosθ = secθ:

From the Pythagorean Identity, we know that tan²θ + 1 = sec²θ. Hence, sec²θ - 1 = tan²θ:

Problem B)

We have:

Factor out a sine:

From the Pythagorean Identity, sin²θ + cos²θ = 1. Hence, sin²θ = 1 - cos²θ:

Distribute:

Problem C)

We have:

Recall that cos2θ = cos²θ - sin²θ and that sin2θ = 2sinθcosθ. Hence:

From the Pythagorean Identity, sin²θ + cos²θ = 1 so cos²θ = 1 - sin²θ:

Cancel:

By definition:

126 maybe. sorry