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if cos theta = 4/7 and csc theta < 0, what is sin theta and tan theta?

 May 28, 2016
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If the cos of an angle is positive, the angle will be in either the first quadrant or the fourth quadrant.

If the csc of an angle is negative (since csc = 1/sin), the sin will also be negative and the sin is negative in either the third quadrant or the fourth quadrant.

 

Since cos(t) = 4/7 and csc(t) < 0, tthe angle t must be in the fourth quadrant.

 

Since cos = x/r and cos(t) = 4/7,  x = 4 and r = 7.

Using the Pythagorean Theorem:  x2 + y2  =  r2    --->   42 + y2  =  72​   --->   16 + y2  =  49   --->   y2  =  33

So, either  y = sqrt(33)  or  y  =  - sqrt(33).

Since the angle is in the fourth quadrant:  y  =  -sqrt(33).

 

sin = y/r   --->   sin(t)  =  -sqrt(33) / 7

tan = y/x   --->   tan(t)  =  -sqrt(33) / 4

 May 28, 2016

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