document.write( "Question 1171626: cos(a) =-4/5 and a is in quadrant II and sin(b)=5/13 and b is in quadrant II. Find cos(a+b)
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cos(a) =-4/5 and a is in quadrant II and sin(b)=5/13 and b is in quadrant II. Find cos(a+b)
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cos (a + b) = cos (a) cos (b) - sin (a) sin (b)
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document.write( "From above, it's obvious that we need cos (b) and sin (a).
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document.write( "Given , and that ∡a is in the 2nd quadrant, we should realize that we're dealing with a 3-4-5 PYTHAGOREAN TRIPLE, which means that .
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document.write( "Likewise, given , and that ∡b is in the 2nd quadrant, we should realize that we're dealing with a 5-12-13 PYTHAGOREAN TRIPLE, which means that .
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document.write( "We now have:  \n" );
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