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Prove that (i) " sin " 80^(@) "cos...

Prove that
`(i) " sin " 80^(@) "cos " 20^(@) - " cos " 80^(@) " sin " 20^(@) =(sqrt(3))/(2)`
`(ii) " cos " 45^(@) " cos " 15^(@) - " sin " 45^(@) " sin " 15^(@) = (1)/(2)`
`(iii) " cos " 75^(@) " cos " 15^(@) + " sin " 75^(@) " sin " 15^(2)= (1)/(2)`
`(iv) " sin " 40^(@) " cos " 20^(@) " + cos " 40^(@) " sin " 20^(@) =(sqrt(3))/(2)`
`(v) " cos " 130^(@) " cos " 40^(@) l + " sin " 130^(@) " sin " 40^(@) =0`

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