If `A=([4,2],[5,6])` then `|A'|` is equal to

If A=[(1,2,8)],B=[(4),(5),(6)] , and C=[(0,2,0)] and D=[(5),(2),(4)] , then AB + CD is equal to

5(1/6) // 9/2 is equal to:

In a DeltaABC , if a = 4, b = 5 , c = 6 then angle C is equal to

if s is sum of 5/((1^2).(2^2).3)+8/((2^2).(3^2).4)+11((3^2).(4^2).5)+14/((4^2).(5^2).6)+...oo then 4S is equal to: