Given sin(−θ)=−1/4 and tanθ =√15 / 15

What is the value of cosθ ?

A) −√15 / 4

B) −√15 / 60

C) √15 / 4

D) √15 / 60

jjennylove Nov 17, 2018

#1**+2 **

Note.... sin (-θ) = -sin(θ)

And tanθ =√15 / 15 = 1 / √15

So

-sin (θ) = -1/4 ⇒ sin (θ) = 1/4

And

tan (θ) = sin (θ) / cos(θ) rearrange as

cos (θ) = sin (θ) / tan (θ) = (1/4) / (1/ √15) = (1/4) * (√15 / 1) = √15 / 4 ⇒ C

CPhill Nov 17, 2018

#2**+1 **

Much more easier then I anticipated. I was thinking it was that one but I found it more diffuclt but seeing the steps you used which are more simple . Thank you

jjennylove
Nov 17, 2018

#3**+1 **

Thanks....sometimes it helps to "un-rationalize" the denominator on those square root ratios ....[if that's even a word.....LOL!!!! ]

CPhill
Nov 17, 2018

#4**+2 **

I guess you could consider it to be a rationalization of the numerator.

TheXSquaredFactor
Nov 17, 2018