Answers

2015-12-28T00:39:12+05:30
ATQ,
a +3d=0                        ..............(i)
also,
11th term of any A.P is a+10d
3(a+10d)=X     
3a+30d=X
a+3d+a+3d+a+24d=X   (It can be written in this manner)
0+0+a+24d=x           (from i)
a+24d=X     .....................(ii)
and we know that 
25th term of any A.P is a+24d
so 3(a+10d)=a+24d
hence proved

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