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Math Help - calculating cos(A+B)

  1. #1
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    calculating cos(A+B)

    If cos A = 1/3 with 0 < A< pi/2, and sinB=1/4, with pi/2<B<pi. calculate cos(A+B).

    My answer is (-(sqrt15)-2(sqrt2))/12
    But the back of the book says the answer is (-(sqrt15)+2(sqrt2))/12

    Am I wrong or the back? Please explain
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by skeske1234 View Post
    If cos A = 1/3 with 0 < A< pi/2, and sinB=1/4, with pi/2<B<pi. calculate cos(A+B).

    My answer is (-(sqrt15)-2(sqrt2))/12
    But the back of the book says the answer is (-(sqrt15)+2(sqrt2))/12

    Am I wrong or the back? Please explain
    you are correct
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