Answer:
cosθ₁ = - [tex]\frac{5}{13}[/tex]
Step-by-step explanation:
Given
sinθ₁ = - [tex]\frac{12}{13}[/tex] = [tex]\frac{opposite}{hypotenuse}[/tex]
This is a 5- 12- 13 right triangle
with opposite = 12, adjacent = 5 and hypotenuse = 13
Given θ₁ is in the 3rd quadrant where cosθ₁ < 0 , then
cosθ₁ = - [tex]\frac{adjacent}{hypotenuse}[/tex] = - [tex]\frac{5}{13}[/tex]
