find sum of last 15 terms of ap with a=2 and d=2 the total terms are 25
Answers
Answered by
0
a = 2
d = 2
n = 25
L = a + (n-1) d
L = 2 + (25 - 1)2
L = 2 + 24×2
L = 2 + 48
L = 50
Now,
Arrange the terms in descending order.
50, 48, 46......
a = 50
d = - 2
S25 = 25/2 [ 2 × 50 + (25-1) (-2)]
= 25 /2 [ 100 + 24 (-2)]
= 25/2 [ 100 - 48]
= 25 × 52 / 2
= 25 × 26
= 400
d = 2
n = 25
L = a + (n-1) d
L = 2 + (25 - 1)2
L = 2 + 24×2
L = 2 + 48
L = 50
Now,
Arrange the terms in descending order.
50, 48, 46......
a = 50
d = - 2
S25 = 25/2 [ 2 × 50 + (25-1) (-2)]
= 25 /2 [ 100 + 24 (-2)]
= 25/2 [ 100 - 48]
= 25 × 52 / 2
= 25 × 26
= 400
Similar questions