Use the given conditions to find the exact values of sin2u, cos2u, and tan2u  using double angle formulas. cosu = -4/5, pi/2 < u < pi

Answers:     sin 2u = -24/25    cos 2u = 7/25    tan 2u = -24/7======    we need to find the exact value of sin u and tan uwe are given that angle u is in quadrant 2.in quadrant 2, sine is positive and cosine is negative.since      draw a point in quadrant 2 with an x-coordinate of -4. the length of the terminal arm of the angle should have a length of 5. (r is a distance and is never negative; the negative goes to the x-coordinate.)  calculate y using pythagorean theorem.  see attachment. we get      since  x = -4, y = 3, and tan u = y/x, we have    ======sine double angle identity    since  and  , substitute in    sin 2u = -24/25======cosine double angle identity:     cos 2u = 7/25======tangent double angle identitywith tan u = -3/4        fraction division is just multiplying by reciprocal    tan 2u = -24/7

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