document.write( "Question 947064: Given sin(alpha) = -8/9 and pi < alpha < 3pi/2 and sin(beta) = -7/8 and beta is in Quadrant III. Use sum and difference formulas to find Sin(alpha + beta)\r
\n" ); document.write( "\n" ); document.write( "I've been stuck on this one for awhile and was hoping someone could help me out,
\n" ); document.write( "Thanks! \n" ); document.write( "
Algebra.Com's Answer #577762 by lwsshak3(11628)\"\" \"About 
You can put this solution on YOUR website!
Given sin(alpha) = -8/9 and pi < alpha < 3pi/2 and sin(beta) = -7/8 and beta is in Quadrant III. Use sum and difference formulas to find Sin(alpha + beta)
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\n" ); document.write( "sina=-8/9
\n" ); document.write( "cosa=-√(1-sin^2(a))=-√(1-(64/81))=-√(17/81)=-√17/9
\n" ); document.write( "sinb=-7/8
\n" ); document.write( "cosb=-√(1-sin^2(b))=-√(1-(49/64))=-√(15/64)=-√15/8
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\n" ); document.write( "sin(a+b)=sinacosb+cosasinb=-8/9*-√15/8+√17/9*-7/8=8√15/72+7√17/72=(8√15+7√17)/72
\n" ); document.write( "Check:
\n" ); document.write( "sina=-8/9 (Q3)
\n" ); document.write( "a≈242.73˚
\n" ); document.write( "sinb=-7/8 (Q3)
\n" ); document.write( "b≈241.04˚
\n" ); document.write( "a+b≈483.77˚
\n" ); document.write( "sin(a+b)≈sin(483.77)≈0.8312..
\n" ); document.write( "exact value:=(8√15+7√17)/72≈0.8312.. \n" ); document.write( "
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