1.

A circular ring of radius 3cm hangs horizontally form a point 4cm vertically above the centre by 4 strings attached at equal intervals to its circumference. If the angle between two consecutive strings be `theta` , then `costheta` is equal to(A)`4/5`(B) `4/(25)`(C) `(16)/(25)`(D) none of these

Answer» OP=4cm
OA=OB=OC=OD=3cm
`(OA)^2+(OP)^2=(AP)^2`
`AP^2=3^3+4^2=25`
`AP=5cm`
AP=BP=DP=CP=5cm
`AB^2+BC^2=AC^2`
`2AB^2=6^2`
`AB=6/sqrt2=3sqrt2`
`AB=BC=CD=AD=3sqrt2cm`
`sin(theta/2)=1/2*(BC)/(BP)=(3sqrt2)/5=3/(5sqrt2)`
`cos2A=1-2sin^2A`
`costheta=1-2(9/(25*2))`
`costheta=16/25`
Option D is correct.


Discussion

No Comment Found

Related InterviewSolutions