Alberta Free Tutoring And Homework Help For Math 30-1


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A and B are in quadrant 1. Sin A = (4/5) and cos B = (7/9). Give an exact value for Sin (A+B).

6 years ago

Answered By Charles S

Sin(A+B) needs to be expanded using the identity Sin(A+B) = Sin(A)Cos(B) + Cos(A)Sin(B).  As you can see, we weren't given Cos(A) or Sin(B) in the question.  See the whiteboard on how I obtained those values.

Then all you have to do is substitute the values in:

  $\left(\frac{4}{5}\right)\left(\frac{7}{9}\right)+\left(\frac{3}{5}\right)\left(\frac{4\sqrt{2}}{9}\right)$(45 )(79 )+(35 )(429 )  

And simplify

 $\frac{28}{45}+\frac{12\sqrt{2}}{45}=\frac{28+12\sqrt{2}}{45}$2845 +12245 =28+12245  

Attached Whiteboard:

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