# NCERT Class 11-Math's: Exemplar Chapter 3 Trigonometric Functions Part 11

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**Question 10:**

If

**Answer:**

Given,

As we have to prove:

if we find out the expression of sin and tan in terms of and , we can get the desired expression to be proved.

Adding equation 1 and 2 to get the value of .

Similarly, on subtracting equation 2 from 1, we get-

Multiplying equation 3 and

Hence,

**Question 11:**

If then prove that

**Answer:**

To prove:

We know that:

Hence,

**Question 12:**

If then prove that

**Answer:**

To Prove:

Given,

t:

Hence,

**Question 13:**

If then show that [Hint: Use componendo and Dividendo]

**Answer:**

To prove:

Given,

Applying componendo – dividendo rule, we get-