20. Evaluate cos 240°.
Answers
Answered by
2
The reference angle for
240
∘
is
60
∘
(since
240
∘
=
180
∘
+
60
∘
)
60
∘
is an angle of one of the standard triangles with
cos
(
60
∘
)
=
1
2
240
∘
is in the 3rd quadrant so (either by CAST or noting that the "x-side" of the associate triangle is negative)
cos
(
240
∘
)
=
−
cos
(
60
∘
)
cos(240∘)
=
−1/2
Answered by
7
HEY MATE...!!
60∘ is an angle of one of the standard triangles with cos(60∘)=12. 240∘ is in the 3rd quadrant .
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