The sum of the seriesa-(a+d)+(a+2d)-(a+3d)+.............. up to 50 terms is
-50d
25d
a+50d
-25d
Explanation for correct option
Given:a-(a+d)+(a+2d)-(a+3d)+..............
⇒a-(a+d)+(a+2d)-(a+3d)+..............⇒a-a-d+a+2d-a-3d+...........⇒(a-a)+(a-a)+.........+(2d-d)+(4d-3d)+(6d-5d)+.........(48d-47d)-49d
⇒d+d+d+.......... upto 25 terms-49d
⇒24d-49d⇒-25d
Hence, OptionD is correct.
The sum of the series a-(a+d)+(a+2d)-(a-3d)+....upto (2n+1) terms is
Which of the following series forms an AP?
(i)a–2d,a–d,a,a+d,a+2d
(ii)a,a+d,a+2d,a+3d,a+4d
(iii)a–3d,a–d,a+d,a+3d