SOLUTION: Given that sinx = 3/5 and cosy = 7/25, with x and y both being Quadrant I angles, find cos(x + y).

Question 1138863: Given that sinx = 3/5 and cosy = 7/25, with x and y both being Quadrant I angles, find cos(x + y).
Found 3 solutions by Alan3354, ikleyn, MathTherapy:
Answer by Alan3354(69443)   (Show Source): You can put this solution on YOUR website!
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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Look up "Half angle formulas" on Wikipedia.
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I've discovered that I can no longer remember all those formulas.
There are 100's or 1000's of them.
Answer by ikleyn(52931)   (Show Source): You can put this solution on YOUR website!
.

You can find many similar solved problems in my lessons
    - Calculating trigonometric functions of angles
    - Advanced problems on calculating trigonometric functions of angles
    - Evaluating trigonometric expressions
in this site.

Consider these lessons as your textbook, handbook, tutorials and (free of charge) home teacher.

Read them attentively, and then solve your problem on your own.

Answer by MathTherapy(10559)   (Show Source): You can put this solution on YOUR website!

Given that sinx = 3/5 and cosy = 7/25, with x and y both being Quadrant I angles, find cos(x + y).

cos (x + y) = cos (x) cos (y) - sin (x) sin (y)
You need to recognize that signifies a classic 3-4-5 PYTHAGOREAN TRIPLE, and therefore,
The same goes for as this too signifies a classic 7-24-25 PYTHAGOREAN TRIPLE, which means that,
Therefore, cos (x + y) = cos (x) cos (y) - sin (x) sin (y) becomes:
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