(i) a = 10, d = 10

(ii) a = -2, d = 0

(iii) a = 4, d = -3

(iv) a = -1, d = 1/2

(v) a = -1.25, d = -0.25

**Solution:**

**(i) a = 10, d = 10**

Let us consider, the AP as a_{1}, a_{2}, a_{3}, a_{4}, a_{5} …

a_{1} = a = 10

a_{2} = a_{1 }+ d = 10 + 10 = 20

a_{3} = a_{2 }+ d = 20 + 10 = 30

a_{4} = a_{3 }+ d = 30 + 10 = 40

a_{5} = a_{4 }+ d = 40 + 10 = 50

And so on…

Therefore, the A.P. series will be 10, 20, 30, 40, 50 …

The first four terms of this A.P. will be 10, 20, 30, and 40.

**(ii) a = – 2, d = 0**

Let us consider, the AP as a_{1}, a_{2}, a_{3}, a_{4}, a_{5} …

*a*_{1} = *a* = -2

*a*_{2} = *a*_{1 }+ *d* = – 2 + 0 = – 2

*a*_{3} = *a*_{2 }+ d = – 2 + 0 = – 2

*a*_{4} = *a*_{3 }+ *d* = – 2 + 0 = – 2

Therefore, the A.P. series will be – 2, – 2, – 2, – 2 …

The first four terms of this A.P. will be – 2, – 2, – 2 and – 2.

**(iii) a = 4, d = – 3**

Let us consider, the AP as a_{1}, a_{2}, a_{3}, a_{4}, a_{5} …

*a*_{1} = *a* = 4

*a*_{2} = *a*_{1 }+ *d* = 4 – 3 = 1

*a*_{3} = *a*_{2 }+ *d* = 1 – 3 = – 2

*a*_{4} = *a*_{3 }+ *d* = -2 – 3 = – 5

Therefore, the A.P. series will be 4, 1, – 2 – 5 …

The first four terms of this A.P. will be 4, 1, – 2, and – 5.

**(iv) a = – 1, d = 1/2**

Let us consider, the AP as a_{1}, a_{2}, a_{3}, a_{4}, a_{5} …

*a*_{2} = *a*_{1. }+*d* = -1 + 1/2 = -1/2

*a*_{3} = *a*_{2 }+ *d* = -1/2 + 1/2 = 0

*a*_{4} = *a*_{3 }+ *d* = 0 + 1/2 = 1/2

Thus, the A.P. series will be-1, -1/2, 0, 1/2

The first four terms of this A.P. will be -1, -1/2, 0, and 1/2.

**(v) a = – 1.25, d = – 0.25**

Let us consider, the AP as a_{1}, a_{2}, a_{3}, a_{4}, a_{5} …

*a*_{1} = *a* = – 1.25

*a*_{2} = *a*_{1} + *d* = – 1.25 – 0.25 = – 1.50

*a*_{3} = *a*_{2} + *d* = – 1.50 – 0.25 = – 1.75

*a*_{4} = *a*_{3} + *d* = – 1.75 – 0.25 = – 2.00

Therefore, the A.P series will be 1.25, – 1.50, – 1.75, – 2.00 ……..

The first four terms of this A.P. will be – 1.25, – 1.50, – 1.75, and – 2.00.