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anonymous
 5 years ago
Use identities (no calculators) to find the exact value for (sin 9)(sin 36)(cos 9)(cos 36)
anonymous
 5 years ago
Use identities (no calculators) to find the exact value for (sin 9)(sin 36)(cos 9)(cos 36)

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anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0how can you play with those angles to get an angle for which there is an exact value

anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0does this equals cos 45?

anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0\[\sin \theta = \cos 90  \theta\]

anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0How do I figure out if its positive of negative

anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0sines, cosines and tangents in the first quadrant (090 degrees) are all positive

anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0i've just checked my maths formula book and the given expression = cos(9 + 36) not cos (9+36) so the correct answer is (1/sqrt2)

anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0this is not the formula for \[cos(a+b)\] but it is its negative.

anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0of course 9+36=36+9=45

anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0but the formula for \[cos(a+b)=cos(a)cos(b)sin(a)sin(b)\]

anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0and \[sin(a)sin(b)cos(a)cos(b)=(cos(a)cos(b)sin(a)sin(b)\] that is why you had to change the sign from \[\frac{\sqrt{2}}{2}\]to \[\frac{\sqrt{2}}{2}\]
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