document.write( "Question 1138863: Given that sinx = 3/5 and cosy = 7/25, with x and y both being Quadrant I angles, find cos(x + y). \n" ); document.write( "
Algebra.Com's Answer #756789 by MathTherapy(10557)\"\" \"About 
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\n" ); document.write( "Given that sinx = 3/5 and cosy = 7/25, with x and y both being Quadrant I angles, find cos(x + y).
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cos (x + y) = cos (x) cos (y) - sin (x) sin (y)
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document.write( "You need to recognize that \"matrix%281%2C5%2C+sin+%28x%29%2C+%22=%22%2C+3%2F5%2C+%22=%22%2C+O%2FH%29\" signifies a classic 3-4-5 PYTHAGOREAN TRIPLE, and therefore, \"matrix%281%2C3%2C+cos+%28x%29%2C+%22=%22%2C+4%2F5%29\"
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document.write( "The same goes for \"matrix%281%2C5%2C+cos+%28y%29%2C+%22=%22%2C+7%2F25%2C+%22=%22%2C+A%2FH%29\" as this too signifies a classic 7-24-25 PYTHAGOREAN TRIPLE, which means that, \"matrix%281%2C3%2C+sin+%28y%29%2C+%22=%22%2C+24%2F25%29\"
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document.write( "Therefore, cos (x + y) = cos (x) cos (y) - sin (x) sin (y) becomes:  \n" );
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