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If sin(x+20^0)=2sinxcos40^0,where in (0,...

If `sin(x+20^0)=2sinxcos40^0,where in (0,pi/2),` then which of the following hold(s) good? (a)`cos2x=1/2` (b) `cos e c4x=2` (c)`secx/2=sqrt(6)-sqrt(2)` (d) `tanx/2=(2-sqrt(3))`

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`sinxcos20+cosxsin20=2sinxcos40`
`cosxsin20=sinx(2cos40-cos20)`
`tanx=(sin20)/(cos40+(cos40-cos20))`
`=(sin20)/(cos40+2sin30*sin(-10)`
`=(sin20)/(sin50-sin10)`
`=sin20/(2cos30sin20)`
`tanx=1/sqrt3`
`x=30`
...
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