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

Explanation

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`

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