1.

Shown that : `tan48^(@)tan23^(@)tan42^(@)tan67^(@)=1`

Answer» L.H.S. `=tan48^(@)tan23^(@)tan42^(@)tan67^(@)`
`=tan48^(@)tan23^(@)tan(90^(@)-48^(@))tan(90^(@)-23^(@))`
`=tan48^(@)tan23^(@)cot48^(@)cot23^(@)`
`=tan48^(@)tan23^(@)*(1)/(tan48^(@))*(1)/(tan23^(@))=1=R.H.S`.


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