Trigo

• bonkysleuth

  11 May 09, 15:07

  Find the values of cos 2A and tan 2A.

   

  cot A = 2 and 90deg< A < 270 deg.

  I got-3/5 and -4/3 respectively. the answer says it is without the negative sign. Am I right or am i wrong?

  thanks a lot

• wee_ws

  11 May 09, 15:23

  Hi,

    cot A = 2 implies that tan A = 1/2, so A is in the 3rd quadrant.

    Then cos A = -2 / sqrt(5) and with it, you can find cos 2A which is 3/5.

    Do try again and understand where you made a mistake. Thanks!

  Cheers,
  Wen Shih