document.write( "Question 1023822: when cot a = 2/5 and cos b = -3/5 find cos(a+b) \n" ); document.write( "
Algebra.Com's Answer #639389 by Alan3354(69443)\"\" \"About 
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when cot a = 2/5 and cos b = -3/5 find cos(a+b)
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\n" ); document.write( "Angle A could be in Q1 or Q3, not specified.
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\n" ); document.write( "Find sin(A) & cos(A):
\n" ); document.write( "tan = 1/cot
\n" ); document.write( "tan(A) = y/x = 5/2
\n" ); document.write( "r = sqrt(5^2+2^2) = sqrt(29)
\n" ); document.write( "cos = x/r
\n" ); document.write( "cos(A) = 2sqrt(29)/29
\n" ); document.write( "sin = sqrt(1 - cos^2)
\n" ); document.write( "sin(A) = sqrt(783)/29 = 3sqrt(87)/29
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\n" ); document.write( "Find sin(B)
\n" ); document.write( "sin = sqrt(1 - cos^2)
\n" ); document.write( "sin(B) = 4/5
\n" ); document.write( "Here again, B could be in Q2 or Q3, not given.
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\n" ); document.write( "cos(A+B) = cos(A)cos(B) - sin(A)sin(B)
\n" ); document.write( "= (2sqrt(29)/29)*(-3/5) - (3sqrt(87)/29)*(4/5)
\n" ); document.write( "= \"%28-6sqrt%2829%29+-+12%2Asqrt%283%29%2Asqrt%2829%29%29%2F145\"\r
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