Trig Identities

Question

Suppose that t  is in the third quadrant and that sint = -3/7. What is the value of cost?

Answer 1

sint = opposite side over hypotenuse = -3/7. hypotenuse = 7

cost = adjacent side over hypotenuse

adjacent side= -sqr(7^2 -3^2) = -sqr(49-9)= sqr40 = -2sqr10. take the negative square root because t is in quadrant III

cost = -2sqr10/7