document.write( "Question 769552: tan α =15/8 , π < α <3pi/2 ; cos β = -21/29 , pi/2 < β < π Find tan (α + β).
\n" ); document.write( "a) 155/468
\n" ); document.write( "b) 468/493
\n" ); document.write( "c)-11/39
\n" ); document.write( "d) 155/493 \n" ); document.write( "
Algebra.Com's Answer #468920 by lwsshak3(11628)\"\" \"About 
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tan α =15/8 , π < α <3pi/2 ; cos β = -21/29 , pi/2 < β < π Find tan (α + β)
\n" ); document.write( "use a for α
\n" ); document.write( "use b for β
\n" ); document.write( "..
\n" ); document.write( "tan(a+b)=(tan a+tan b)/(1-tan a* tan b)
\n" ); document.write( "cos b=-21/29
\n" ); document.write( "sin b=√(1-cos^2b)=√(1-(441/841))=√(400/841)=20/29
\n" ); document.write( "tan b=sin b/cos b=-20/21
\n" ); document.write( "tan(a+b)=(15/8-20/21)/(1-(15/8)*(-20/21))
\n" ); document.write( "tan(a+b)=(21*15-8*20)/168)/(1+300/168)
\n" ); document.write( "=((315-160)/168))/(468/168)
\n" ); document.write( "=155/168/(468/168)
\n" ); document.write( "=155/468
\n" ); document.write( "calculator check:
\n" ); document.write( "tan a=15/8
\n" ); document.write( "a=≈61.9275º
\n" ); document.write( "cos b=-21/29
\n" ); document.write( "b≈136.3972
\n" ); document.write( "a+b≈198.3247
\n" ); document.write( "tan(a+b)=tan(198.3247)≈0.3312..
\n" ); document.write( "Exact answer as calculated=155/468≈0.3312.. \n" ); document.write( "
\n" );