The radius of circular section in which the sphere |→r|=5 is cut by the plane →r⋅(^i+^j+^k)=3√3, is equal to
A
4.00
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B
4
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C
4.0
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Solution
Let A be the foot of perpendicular from the centre O to the plane →r⋅(^i+^j+^k)−3√3=0
Then, |OA|=∣∣
∣∣0⋅(^i+^j+^k)−3√3|^i+^j+^k|∣∣
∣∣=3√3√3=3
(perpendicular distance of a point from the plane)
If, P is any point on the circle, then P lies on the plane as well as on the sphere,
So, OP= radius of sphere =5
Now, AP2=OP2−OA2=52−32=16 ⇒AP=4