Answered

if tanФ[tex] \frac{2}{3} [/tex] & theta is in quadrant III, find cosФ.
clue: write cosФ in terms of tanФ from tan²Ф+1= sec²Ф

Sagot :

Cheahjimmyviz
if tanФ = 2/3      find  cos Ф   
using the identity        tan²Ф+ 1=  sec² Ф
we have
               ( 2/3)² + 1 =    1/cos²Ф          / sec²= 1/cos²Ф
                 4/9+1 = 13/9 =1/cos²Ф
                 cos²Ф = 9/13
                 cosФ =  √(9/13)  =  + or -  3/√13
the answer is - 3/√13 only since Ф is in the third quadrant