Prove that csc⁡2x+cot⁡2x=cot⁡x\csc 2x + \cot 2x = \cot x. Hence, solve csc⁡x+cot⁡x=3\csc x + \cot x = \sqrt{3} where 0≤x≤2π0 \le x \le 2\pi.

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Worked solution

3(a)

1. Express the left-hand side (LHS) in terms of sine and cosine.

LHS=csc⁡2x+cot⁡2x\text{LHS} = \csc 2x + \cot 2x
=1sin⁡2x+cos⁡2xsin⁡2x= \frac{1}{\sin 2x} + \frac{\cos 2x}{\sin 2x}

2. Combine the terms into a single fraction.

=1+cos⁡2xsin⁡2x= \frac{1 + \cos 2x}{\sin 2x}

3. Apply double angle formulae to express the numerator and denominator in terms of single angles.

Using cos⁡2x=2cos⁡2x−1\cos 2x = 2\cos^2 x - 1 and sin⁡2x=2sin⁡xcos⁡x\sin 2x = 2\sin x \cos x:
=1+(2cos⁡2x−1)2sin⁡xcos⁡x= \frac{1 + (2\cos^2 x - 1)}{2\sin x \cos x}

4. Simplify the expression to obtain the right-hand side (RHS).

=2cos⁡2x2sin⁡xcos⁡x= \frac{2\cos^2 x}{2\sin x \cos x}
=cos⁡xsin⁡x= \frac{\cos x}{\sin x}
=cot⁡x= \cot x
=RHS (shown)= \text{RHS (shown)}

Answer

Proof completed.

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