एक A.P. में,
a = 5, d = 3 और an = 50 दिया है। n और Sn ज्ञात कीजिए।
यहाँ, a = 5, d = 3, an = 50
an = a + (n – 1 )d
⇒ 50 = 5 + (n – 1) x 3
⇒ 50 – 5 = 3 x (n – 1)
⇒ 45 = 3 x (n – 1)
= 8 x [ 10 + 15 x 3]
= 8 x 10 + 45
= 8 x 55 = 440
n = 16
Sn = S16 = 440