# Algebra 2/ Trigonometry

posted by
**Moe** on
.

If cos y = -4/5 when 90°≤ y ≤ 180° what is the value of cos 2y?

posted by
**Moe** on
.

If cos y = -4/5 when 90°≤ y ≤ 180° what is the value of cos 2y?