Answer:
The angle
3
π
4
is in the 2nd quadrant
where the cos ratio has a negative value. Now the related acute angle for
3
π
4
is
π
4
then
cos
(
3
π
4
)
=
−
cos
(
π
4
)
Using the 45-45-90 degree triangle with sides 1 , 1 ,
√
2
where
cos
45
∘
=
cos
(
π
4
)
=
1
√
2
⇒
cos
(
3
π
4
)
=
−
cos
(
π
4
)
=
−
1
√
2
Step-by-step explanation:
1√2 answer
