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Without using trigonometric tables , pro...

Without using trigonometric tables , prove that :
(i) `tan20^(@)tan40^(@) tan45^(@)tan50^(@)tan70^(@)=1`
(ii) `tan1^(@) tan2^(@)tan60^(@)tan88^(@)tan89^(@)=sqrt(3)`
(iii) `cot5^(@)cot10^(@)cot30^(@)cot80^(@)cot85^(@)=sqrt(3)`
(iv) `4sin10^(@)sin20^(@)sin30^(@)sec70^(@)sec80^(@)=2`

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