Question

If the first and the last terms of an arithmetic series are 10 and 62, show that the sum of the series varies directly as the number of terms.

Answer 1

hey..

sn = n/2 [a + an]
sn = n/2 [10 + 62]
sn = n/2 [72]
sn = 36n

Therefore the sum of series varies directly as the number of terms