Find S10 if a = 6 and d = 3.

3. Find S10 if a = 6 and d = 3.

Sol. For an A.P. a = 6, d = 3

Sn = n/2 [2a + (n – 1) d]

∴  S10 = 10/2 [2a + (10 – 1) 1]

∴  S10 = 5 [2 (6) + 9 (3)]

∴  S10 = 5 (12 + 27)

∴  S10 = 5 (39)

∴  S10 = 195