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Two circles of radii 4cm and 1cm touch e...

Two circles of radii 4cm and 1cm touch each other externally and `theta` is the angle contained by their direct common tangents. Find `sin (theta/2)+cos(theta/2) dot`

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`B'D||C_1C_2`
`B'C_2=C_1D`
`AD=4-1=3cm`
`B'D=5cm`
`AB'=4cm`
`sin(theta/2)+cos(theta/2)`
`3/5+4/5=7/5`.
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