Sum of first 30terms of an a.P. are equal to first 20 terms.show that the sum of first 50terms of the same ap is zero
sum(30) = sum(20)
15(2a + 29d) = 10(2a + 19d)
divide by 5 and expand
6a + 87d = 4a + 38d
2a = -49d
a = -49/2
sum(50) = 25( 2(-49/2)d + 49d)
= 25(0)
= 0