What is cos if sin=-0.8 and is in Quadrant IV?r Trigonometry 1 Answer Liam P. May 4, 2018 #cos(arcsin(-4/5))# Explanation: Since #-4/5# isn't found on any of the special triangles, the best you can do is to isolate for theta and type it into your calculator. You know that cos will be positive since you are in quadrant IV. Answer link Related questions How do I determine the molecular shape of a molecule? What is the lewis structure for co2? What is the lewis structure for hcn? How is vsepr used to classify molecules? What are the units used for the ideal gas law? How does Charle's law relate to breathing? What is the ideal gas law constant? How do you calculate the ideal gas law constant? How do you find density in the ideal gas law? Does ideal gas law apply to liquids? Impact of this question 494 views around the world You can reuse this answer Creative Commons License