Q. 24.3( 226 Votes )
Write first four terms of the AP, when the first term a and the common difference d aregiven as follows:
(i) 
(ii) 
(iii) 
(iv) 
(v) 
Answer :
(i) Here, first term a1 = 10 and common difference, d = 10
Hence,
2nd term a2 = a1 + d
= 10 + 10
= 20
3rd term a3 = a1 + 2d
= 10 + 2 x 10
= 30
4th term a4 = a1 + 3d
= 10 + 30
= 40
Therefore,
first four terms of the AP are:
10, 20, 30, 40, ……
(ii) Here,
First term a = -2 and Common difference = 0
Therefore, first four terms of the given AP are:
a1 = - 2, a2 = - 2, a3 = - 2 and a4 = - 2
(iii) Here, first term a1 = 4 and common difference d = - 3
We know that an = a + (n – 1)d, where n = number of terms
Thus, second term a2 = a + (2 – 1)d
a2 = 4 + (2-1)×(-3)
= 4 - 3 = 1
3rd term a3 = a + (3 – 1)d
= 4 + (3-1) × (-3)
= 4 - 6
= -2
4th term a4 = a + (4-1)d
= 4 + (4 - 1) ×( -3)
= 4 - 9 = -5
Therefore,
First four terms of given AP are:
4, 1, - 2, - 5
(iv) We have,
1st term = - 1 and d = 1/2
Hence,
2nd term a2 = a1 + d
= -1 + 1/2
= - 1/2
3rdterm a3 = a1 + 2d
= -1 + 2 * 1/2
= 0
4th term a4 = a1 + 3d
= -1 + 3 * 1/2
= 1/2
Therefore,
The four terms of A.P. are -1, - 1/2, 0, 1/2
(v) We have
1st term = - 1.25 and d = - 0.25
2nd term a2 = a + d
= -1.25 - 0.25
= -1.5
3rd term a3 = a + 2d
= -1.25 + 2 × (-0.25)
= -1.25 - 0.5
= -1.75
4th term a4 = a + 3d
= -1.25 + 3 × (-0.25)
= -2
Therefore, first four terms of the A.P. are: -1.25, -1.5, -1.75 and – 2
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