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If tanA=(1-cosB)/(sinB) , then tan2A=tan...

If `tanA=(1-cosB)/(sinB)` , then `tan2A=tanBdot`

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`tanA = (1-cosB)/sinB`
`=>tanA = (2sin^2(B/2))/(2sin(B/2)cos(B/2))`
`=>tanA = tan(B/2)`
Now, `tan2A = (2tanA)/(1-tan^2A) = (2tan(B/2))/(1-tan^2(B/2)) = tanB`
`:. tan2A = tanB.`
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