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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- June 14th 2009, 05:58 PMskeske1234calculating 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 - June 14th 2009, 06:14 PMJhevon