Question

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

Answer 1

unit circle??

Answer 2

with outt it

Answer 3

ok, u know what is cos 60 ?

Answer 4

pi/3

Answer 5

cos pi/3 = ?

Answer 6

60

Answer 7

lol!
60=pi/3
cos 60 = 0.5
ok ?

Answer 8

ohh ok

Answer 9

sec 240 = 1/ cos 240
cos 240 = cos (180+60)
cos (180+x) = -cos x
now try

Answer 10

what should i try im a lilttle confused

Answer 11

cos (180+x) = -cos x
so
cos 240 = -cos 60 = -0.5
got this ?

Answer 12

i think so

Answer 13

now sec 240 =1/ cos 240 = 1/(-0.5) = -2
ok ?

Answer 14

why did u use cos 60 though?

Answer 15

60 degrees is the reference angle for 240 degrees

Answer 16

because cos 60 is known
60 is standard angle
in unit circle

Answer 17

ok

Answer 18

any more doubts ?