Trig

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If sin = 2/3 and is a second quadrant angle, determine the exact value of sec^2
could be
a. 5/9
b. root5/3
c. 9/4
d. 9/5

Please help.......

  • Trig -

    If sin = 2/3, the side opposite from the angle is 2 and the hypotenuse is 3, since sin is opposite over hypotenuse.

    a^2 + b^2 = c^2. The hypotenuse, 3, is c, and 2 can be a. 3^2 - 2^2 is 5. Since that leaves b^2 = 5, you have to take the root of both sides, so b = root5. That means the adjacent side is root5.

    Cos is adjacent over hypotenuse, so cos is root5 over 3. Sec is cos flipped, so sec is 3/root5 or 3root5/5. When you square that whole thing, you get 9 times 5 (45) divided by 25, which is the same thing as 9/5.

    I hope that helped!

  • Trig -

    sin^2 = 4/9
    cos^2 = 1 - sin^2 = 5/9
    1/cos^2 = sec^2 = 9/5

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