Let a be the first term and d be the common difference of an AP.a4​=a+(n−1)d=a+(4−1)d=a+3dSince 4th term of an AP is zero.a+3d=0or a=−3d ........(1)Similarly,a25​=a+24d=−3d+24d=21d ......(2)a11​=a+10d=−3d+10d=7d .......(3)From (2) and (3), we havea25​=3×a11​Hence proved.