# NCERT Class 11-Math՚S: Chapter 3 Exemplar Trigonometric Functions Part 13 (For CBSE, ICSE, IAS, NET, NRA 2022)

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## Long Answer Type

**Question 20**:

If then prove that

**Answer**:

Given,

prove:

As, LHS

Using:

It involves terms so we need to calculate it first.

Similarly,

Using:

Thus,

**Question 21**:

If , then prove that

**Answer**:

Given,

To prove: .

Applying componendo – dividend, we get

From transformation formula, we know that –

**Question 22**:

Find the value of the expression

**Answer**:

Let,

We know that-