Ifs1=a2+a4+a6+.... upto 100 terms and s2=a1+a3+a5+.... upto 100 terms of a certain A.P., then its common difference is:
Given that,
S1=a2+a4+−−−−−upto100terms.
=[a+(2−1)d]+[a+(4−1)d]+−−−−−upto100terms
=(a+d)+(a+3d)+−−−−−−upto100terms
=(a+a+a+−−−−upto100terms)+(d+3d+5d+−−−−upto100terms)
=100a+d[1002{2(1)+(100−1)×2}]
S1=100a+10000d.......(1)
So,
S2=a1+a3+−−−−−upto100terms.
=[a+(1−1)d]+[a+(3−1)d]+−−−−−upto100terms
=(a+0×d)+(a+2d)+−−−−−−upto100terms
=(a+a+a+−−−−upto100terms)+(0d+2d+4d+−−−−upto100terms)
=100a+d[1002{2(0)+(100−1)×2}]
S1=100a+9900d.......(2)
Then,
S1−S2=100a+10000d−100a−9900d
=100d
S1−S2=100d
d=S1−S2100
Hence, this is the answer.