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Given that 
cos A=(sqrt23)/(5) and 
sin B=(sqrt21)/(6), and that angles 
A and 
B are both in Quadrant I, find the exact value of 
sin(A+B), in simplest radical form.
Answer:

Given that cosA=235 \cos A=\frac{\sqrt{23}}{5} and sinB=216 \sin B=\frac{\sqrt{21}}{6} , and that angles A A and B B are both in Quadrant I, find the exact value of sin(A+B) \sin (A+B) , in simplest radical form.\newlineAnswer:

Full solution

Q. Given that cosA=235 \cos A=\frac{\sqrt{23}}{5} and sinB=216 \sin B=\frac{\sqrt{21}}{6} , and that angles A A and B B are both in Quadrant I, find the exact value of sin(A+B) \sin (A+B) , in simplest radical form.\newlineAnswer:
  1. Use Sine Addition Formula: Use the sine addition formula: sin(A+B)=sin(A)cos(B)+cos(A)sin(B)\sin(A+B) = \sin(A)\cos(B) + \cos(A)\sin(B).\newlineWe need to find sin(A)\sin(A) and cos(B)\cos(B).
  2. Find sin(A)\sin(A) and cos(B)\cos(B): Since AA is in Quadrant I, sin(A)\sin(A) is positive. We can find sin(A)\sin(A) using the Pythagorean identity: sin2(A)+cos2(A)=1\sin^2(A) + \cos^2(A) = 1. We know cos(A)=235\cos(A) = \frac{\sqrt{23}}{5}, so cos2(A)=2325\cos^2(A) = \frac{23}{25}. sin2(A)=1cos2(A)=12325=25252325=225\sin^2(A) = 1 - \cos^2(A) = 1 - \frac{23}{25} = \frac{25}{25} - \frac{23}{25} = \frac{2}{25}. sin(A)=sin2(A)=225=25\sin(A) = \sqrt{\sin^2(A)} = \sqrt{\frac{2}{25}} = \frac{\sqrt{2}}{5}.
  3. Find sin(B)\sin(B) and cos(B)\cos(B): Since BB is in Quadrant I, cos(B)\cos(B) is also positive. We can find cos(B)\cos(B) using the Pythagorean identity: sin2(B)+cos2(B)=1\sin^2(B) + \cos^2(B) = 1. We know sin(B)=216\sin(B) = \frac{\sqrt{21}}{6}, so sin2(B)=2136\sin^2(B) = \frac{21}{36}. cos2(B)=1sin2(B)=12136=36362136=1536=512\cos^2(B) = 1 - \sin^2(B) = 1 - \frac{21}{36} = \frac{36}{36} - \frac{21}{36} = \frac{15}{36} = \frac{5}{12} after simplifying. cos(B)=cos2(B)=512=512=523=5323=156\cos(B) = \sqrt{\cos^2(B)} = \sqrt{\frac{5}{12}} = \frac{\sqrt{5}}{\sqrt{12}} = \frac{\sqrt{5}}{2\sqrt{3}} = \frac{\sqrt{5}\sqrt{3}}{2\cdot3} = \frac{\sqrt{15}}{6} after rationalizing the denominator.
  4. Plug in Values: Now we have sin(A)=25\sin(A) = \frac{\sqrt{2}}{5} and cos(B)=156\cos(B) = \frac{\sqrt{15}}{6}. Plug these values into the sine addition formula: sin(A+B)=sin(A)cos(B)+cos(A)sin(B)\sin(A+B) = \sin(A)\cos(B) + \cos(A)\sin(B). sin(A+B)=(25)(156)+(235)(216).\sin(A+B) = \left(\frac{\sqrt{2}}{5}\right)\left(\frac{\sqrt{15}}{6}\right) + \left(\frac{\sqrt{23}}{5}\right)\left(\frac{\sqrt{21}}{6}\right).
  5. Simplify Expression: Simplify the expression: sin(A+B)=21556+232156\sin(A+B) = \frac{\sqrt{2}\cdot\sqrt{15}}{5\cdot6} + \frac{\sqrt{23}\cdot\sqrt{21}}{5\cdot6}.\newlinesin(A+B)=3030+48330.\sin(A+B) = \frac{\sqrt{30}}{30} + \frac{\sqrt{483}}{30}.
  6. Combine Terms: Combine the terms over a common denominator: sin(A+B)=(30+483)/30\sin(A+B) = (\sqrt{30} + \sqrt{483})/30. Since 483\sqrt{483} can be simplified to 3×161=3×161=3×7×23=3×7×23\sqrt{3\times161} = \sqrt{3}\times\sqrt{161} = \sqrt{3}\times\sqrt{7\times23} = \sqrt{3}\times\sqrt{7}\times\sqrt{23}, we can rewrite the expression. sin(A+B)=(30+3×7×23)/30\sin(A+B) = (\sqrt{30} + \sqrt{3}\times\sqrt{7}\times\sqrt{23})/30.
  7. Simplify Further: Simplify the expression further: sin(A+B)=(30+3723)/30\sin(A+B) = (\sqrt{30} + \sqrt{3}\cdot\sqrt{7}\cdot\sqrt{23})/30.sin(A+B)=(30+3723)/30=(30+3723)/30\sin(A+B) = (\sqrt{30} + \sqrt{3}\cdot\sqrt{7}\cdot\sqrt{23})/30 = (\sqrt{30} + \sqrt{3\cdot7\cdot23})/30.sin(A+B)=(30+3723)/30=(30+483)/30\sin(A+B) = (\sqrt{30} + \sqrt{3\cdot7\cdot23})/30 = (\sqrt{30} + \sqrt{483})/30.
  8. Final Expression: Notice that 483\sqrt{483} was already simplified in a previous step, so we do not need to simplify it again.\newlineThe final expression for sin(A+B)\sin(A+B) is 30+48330\frac{\sqrt{30} + \sqrt{483}}{30}.

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