If tan thelta = - 4/3, what would be cos thelta ?

2 Answers
Mar 4, 2018

#Cos theta= 3/5#

Explanation:

This is a 3, 4, 5 Pythagorean triple triangle in quadrant 4 as sin or y is negative and cos or x is not.

Mar 4, 2018

#cos t = +- 3/5#

Explanation:

Use trig identity:
#cos^2 t = 1/(1 + tan^2 t)#
In this case:
#cos^2 t = 1/(1 + 16/9) = 9/25#
#cos t = +- 3/5.#
There are 2 opposite answers, because t could be either in Quadrant 2, or in Quadrant 4 (tan t < 0).