Advertisements
Advertisements
Question
The sum of 20 and 28 terms of an A.P. are equal. Find the sum of 48 terms of this A.P.
Sum
Advertisements
Solution
S20 = S28
`S_20 = 20/2[2a + (20 - 1)d] = S_28 = 28/2[2a + (28 - 1)d]`
`20/2[2a + 19d] = 28/2[2a + 27d]`
10a + 95d = 14a + 189d
−4a = 94d
a = `(-94d)/4`
a = `(-47d)/2`
2a = −47d
`S_48 = 48/2[2a + 47d]`
= 24[−47d + 47d]
= 24 × 0
= 0
shaalaa.com
Is there an error in this question or solution?
