If in the figure `AB=a,AC=4cm`, while D is the circle of the circle and D is a points betbeen O and B such that `AD_|_BC`.The length (in cm) of OD is

Explanation

OB=OC=0A=R

OD=x

`/_ABD`

`AB^2=BD^2+AD^2-(1)`

`/_ABC`

`AC^2=AB^2+DC^2-(2)`

subtracting equation 2 from equation 1

`a^2-16=(R-x)^2-(R+x)^2`

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