Answer:
See explanation.
Step-by-step explanation:
a) From the triangle, other two angles are equal (90/2) = 45° because the lengths of sides opposite them are also equal.
Therefore,
cos 45° = 1/√2
Note: 45° is in the first quadrant and all Trigonometric are positive there.
b) 315° is in the fourth quadrant and cosine is the only positive trig. there with formula: 360° - theta governing that quadrant.
cos 315° = cos (360°- 315°)
= cos 45°
cos 315° = 1/√2
