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Prove that: t a n 70^0=t a n 20^0+2t a n...

Prove that: `t a n 70^0=t a n 20^0+2t a n 50^0dot`

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`70^(@)=20^(@)+50^(@)`
`rArr tan70^(@)=tan(20^(@)+50^(@))`
`rArr tan70^(@)-tan70^(@)tan20^(@)tan50^(@)=tan20^(@)+tan50^(@)=tan20^(@)+tan50^(@)`
`tan70^(@)-cot20^(@).1/(cot20^(@))tan50^(@)=tan20^(@)+tan50^(@)`
`rArr tan70^(@)-tan50^(@)=tan20^(2)+tan50^(@)`
`rArr tan70^(@)=tan20^(@)+2tan50^(2)` Hence proved.
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