Answer:
Cos 2theta = -3/5
Explanation:
Given that;
tan theta = -2
tan theta = -2/1 = opp/adj
hyp^2 = (-2)^2+1^2
hyp = √4+1
hyp = √5
sin theta = opp/hyp
sin theta = -2/√5
Cos theta = adj/hyp
Cos theta = -2/√5
Cos 2theta = 1-2sin^2 theta
Cos 2theta = 1- 2(-2/√5)^2
Cos 2theta = 1- 2(4/5)
Cos 2theta = 1- 8/5
Cos 2theta = (5-8)/5
Cos 2theta = -3/5