**Question 1.**

Solution:

**Question 2.Solution:**

**Question 3.Solution:**

**Question 4.**

**Solution:**

**Question 5.Find the sum 5 × 7 + 9 × 11 + 13 × 15 + ….. upto n terms.Solution:**

5 × 7 + 9 × 11 + 13 × 15 + ….. upto n terms

Now, 5, 9, 13, … are in A.P. with

rth term = 5 + (r – 1) (4) = 4r + 1

7, 11, 15, ….. are in A.P. with

rth term = 7 + (r – 1) (4) = 4r + 3

∴ 5 × 7 + 9 × 11 + 13 × 15 + …… upto n terms

**Question 6.Solution:**

**Question 7.**

Here, 2, 4, 6,…, 70 are in A.P. with rth term = 2r

and 1, 3, 5, …,69 are in A.P. with rth term = 2r – 1

**Question 8.Find the sum 1 × 3 × 5 + 3 × 5 × 7 + 5 × 7 × 9 + …… + (2n – 1) (2n + 1) (2n + 3)Solution:**

Let S = 1 × 3 × 5 + 3 × 5 × 7 + ….. upto n terms

Here, 1, 3, 5, 7 … are in A.P. with rth term = 2r – 1,

3, 5, 7, 9,… are in A.P. with rth term = 2r + 1,

5, 7, 9, 11,… are in A.P. with rth term = 2r + 3

**Question 9.Solution:**

**Question 10.Solution:**