## Answer (Detailed Solution Below)
Let us consider sequence a1, a2, a3 . an is an A.P. - Common difference d= a2 a1 = a3 a2 = . = an an 1
- nth term of the A.P. is given by an = a + (n 1) d
- nth term from the last is given by an = l (n 1) d
- sum of the first n terms = S = n/2[2a + (n 1) × d]
Or sum of the first n terms = n/2(a + l) Where, a = First term d = Common difference n = number of terms an = nth term l = Last term
Given: 1st term = 4 = a1 9th term = 20 = a9 We know, the formula for nth term of an A.P is an = a1 + (n 1)d a9 = a 1 + (9 1) d a9 = a1 + (8) d 20 = 4 + 8d 16 = 8d d = 2 Now, a15 = a1 + (15 1) d = a1 + (14) d = 4 + 14 × 2 = 32 The 15th term of the A.P = 32 Indias Start Complete Exam Preparation Trusted by 2,48,43,998+ Students ## Video |