निम्नलिखित के मान ज्ञात कीजिए ।
(i) ` cos 135^(@)` (ii) ` sin ( -780^(@))`
(iii) ` tan 240^(@)` (iv) ` ""cosec" "1920^(@)`

Explanation

(i) ` cos 135^(@) = cos ( 90^(@) + 45^(@)`
(ii) ` sin ( -780^(@) ) = -sin 780^(@)`
` = sin ( 2 xx 360^(@) + 60^(@)`
` = - sin 60^(@)`
` = - (sqrt(3))/2`
(iii) ` tan 240^(@) = tan ( 180^(@) + 60^(@)`
` = tan 60^(@) `
` = sqrt(3)`
(iv) ` "cosec" 1920^(@) = "cosec" ( 5 xx 360^(@) + 120^(@)) `
` = csec 120^(@)`
` = "cosec" ( 180^(@) - 60^(@))`
` = 2/(sqrt(3))`