Help, trig question (1 Viewer)

[jannny]

Ok this was a question from the CSSA 2007 trial, and I dont get the answer

Given that sin(theta) = 3/5 and tan(theta) < 0 , find the exact value of cos(theta)

My answer was cos(theta) = 4/5

but the answer is cos(theta) = - (4/5)

thanks.

 

[beentherdunthat]

It's negative, because theta is defined only in quadrant one and two. Not three or four. That is why tan (theta) is negative, because tan is quadrant 3. Thus, Cos (theta) must be negative, as cos is quadrant four.

 

[watatank]

Ok this was a question from the CSSA 2007 trial, and I dont get the answer

Given that sin(theta) = 3/5 and tan(theta) < 0 , find the exact value of cos(theta)

My answer was cos(theta) = 4/5

but the answer is cos(theta) = - (4/5)

thanks.

cos(theta), if it were in the first quadrant would = 4/5 (A/H) because the answer is always positive in that quadrant.

but they told you that tan(theta) is negative, so that must mean the answer is either in 2nd or 4th quadrant. since sin(theta) is positive it must mean it must be in the 2nd quadrant. cos(theta) is negative in the 2nd quadrant, so the answer is negative.

 

[jannny]

thanks a lot guys