# NCERT Class 11-Math՚S: Chapter – 13 Limits and Derivatives Part 4 (For CBSE, ICSE, IAS, NET, NRA 2022)

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**Question 17**:

Evaluate

**Answer**:

We have

**Question 18**:

Evaluate

**Answer**: We have

**Question 19**:

Find the derivative of , by first principle.

**Answer**:

We have

**Question 20**:

Find the derivative of by first principle.

**Answer**: By definition

**Question 21**:

Find the derivative of

**Answer**:

Let

Differentiating both sides with respects to , we get