CBSE Class 10 Answered
S50 == 50 / 2 [ 2a + {50 -1} d ] == 200
25 [ 2a + 49 d ] = 200
[ 2a + 49 d ] = 200 / 25 == 8 ----------(1)
S 100 - S 50 = 100 / 2 [ 2a + ( 100 - 1 ) d ] --- 50 / 2 [ 2a + ( 50 - 1) d ] == 2700
== 50 [ 2a +99d ] -- 25 [ 2a +49 d ] ==2700
= 2 [ 2a + 99d ] - [ 2a + 49 d ] == 2700 / 25 = 108
= 4a + 198 d --2a --49 d ==108
== 2a + 149 d = 108 ---------------(2)
solving (1) & (2)
2a +49 d = 8
2a + 149 d = 108
100 d = 100 =====> d = 1
substituting this value in the equation (1)
2a + 49 (1) == 8
2a == 8 - 49 == --41
a == -- 20 ..5
so the A.P is --20.5 ,, --19.5,,--18.5 ...................... 100 terms