find cosθ if sinθ=-4/5 and is in quad three

Question

solomonzelman · Answer

|dw:1418953636599:dw|can you find the third side?

anonymous · Answer

hey it doesnt matter but from what i seen in the past.. try to construct that triangle using the reference angle. @SolomonZelman

solomonzelman · Answer

will see, this time it is not a necessity though, I see you agree to this. 
it sounds like you are criticizing me, jk  but I know I suck at math....

solomonzelman · Answer

there is a rule:
$\large\color{black}{  a^2+b^2=c^2 }$    (where c is the hypotenuse)

plugging your values:  $\large\color{black}{  a^2+4^2=5^2 }$

fiond te 3rd side.

anonymous · Answer

well with that many fans and  great testimonials i say you rock!!!!! :D... but anyway the reason i suggested it is because im pretty sure he/she is at that stage where their learning co-terminal and reference angles.

anonymous · Answer

your right @magepker728

anonymous · Answer

but im still lost

anonymous · Answer

ok then sinetheta is opposite/hypotenuse in this case u have sinetheta in 3rd quadrant

anonymous · Answer

and costheta is adjecent/hypotenuse we already know the hypotenuse so adjacent is missing .. to find it used the equations salomonzelmen provided

anonymous · Answer

so in other words find a