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Prove that tan 70^(@)=cot70^(@)+2cot40^(...

Prove that `tan 70^(@)=cot70^(@)+2cot40^(@)`

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LHS `=tan70^(@)=tan(20^(@)+50^(@))=(tan20^(@)+tan50^(@))/(1-tan20^(@)tan50^(@))`
or `tan70^(@)-tan20^(@)tan50^(@)tan70^(@)=tan20^(@)+tan50^(@)`
`=cot70^(@) + 2cot40^(@)` =RHS
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