If `2, h_(1), h_(2),………,h_(20)6` are in harmonic progression and `2, a_(1),a_(2),……..,a_(20), 6` are in arithmetic progression, then the value of `a_(3)h_(18)` is equal to

The numbers h_(1),h_(2),h_(3),h_(4),...,h_(10) are in harmonicprogression and a_(1),a_(2),...,a_(10) are in arithmetic progression.If a_(1)=h_(1)=3 and a_(7)=h_(7)=39, thenthe value of a_(4)xx h_(4) is

If a_(1),a_(2),...a_(n) are in H.P then the expression a_(1)a_(2)+a_(2)a_(3)+...+a_(n-1)a_(n) is equal to

If a_(1),a_(2),a_(3),..., are in arithmetic progression,then S=a_(1)^(2)-a_(2)^(2)+a_(3)^(2)-a_(4)^(2)+...-a_(2k)^(2) is equal

If a_(1), a_(2), a_(3),…….,a_(20) are in AP and a_(1) + a_(20) = 45 , then a_(1) + a_(2) + a_(3)+……+a_(20) is equal to

Let a,b be positive real numbers.If aA_(1),A_(2),b be are in arithmetic progression a,G_(1),G_(2),b are in geometric progression,and a,H_(1),H_(2),b are in harmonic progression,show that (G_(1)G_(2))/(H_(1)H_(2))=(A_(1)+A_(2))/(H_(1)+H_(2))