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In a "DeltaA B C prove that tan(("A"+"B"...

In a `"DeltaA B C` prove that `tan(("A"+"B")/2)=cot("C"/2)`

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In any traingle `ABC, angle A+angle B+angle C=180^circ`
`Rightarrow angle A+angle B=180^circ-angle C`
`(Rightarrow angle A+angle B)/2=(180^circ-angle C)/2`
`Rightarrow (angle A+angle B)/2=90^circ-(angle C)/2`
`Rightarrow tan ((angle A+angle B)/2)=tan (90^circ-(angle C)/2)`
`therefore tan ((angle A+angle B)/2)=cot(( angle C)/2)`
Hence proved.
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