Question

Evaluate sec 240Á without using a calculator by using ratios in a reference triangle.

Answer 1

Sec∅ = 1/cos∅
= 1/cos(240)
= 1/cos(180 + 60)
= 1/-cos(60)
= 1/(-1/2)
= -2

Answer 2

60=pi/3
cos 60 = 0.5
sec 240 = 1/ cos 240
 cos 240 = cos (180+60)
cos (180+x) = -cos x
cos (180+x) = -cos x
so
cos 240 = -cos 60
              = -0.5
sec 240 =1/ cos 240
              = 1/(-0.5)
              = -2