Posted by **Amanda** on Thursday, April 19, 2012 at 12:22pm.

Evaluate the expression under the given conditions.

sin (A+B); tan A= 12/5, A in quadrant 3, sin B= -3sqrt(10)/10, B in quadrant 4.

- Pre-Calc Help!!!!!!!! -
**Steve**, Thursday, April 19, 2012 at 12:33pm
in QIII, sin and cos are both negative.

You have a 5-12-13 triangle, so

sinA = -12/13

cosA = -5/13

in QIV, cos is positive.

You have a 3-1-√10 triangle, so

cosB = 1/√10

Now apply the addition formula

sin(A+B) = sinAcosB + cosAsinB

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