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September 30, 2014

September 30, 2014

Posted by **cheyanne** on Friday, February 24, 2012 at 1:20am.

tan (-15 degrees)

2) Rewrite the following expression as a trigonometric function of a single angle measure.

cos 3x cos 4x - sin 3x sine 4x

- TRIG/ALGEBRA -
**Reiny**, Friday, February 24, 2012 at 8:42am1.

tan 15 = tan(45-30)

= (tan45-tan30)/(1 + tan45tan30)

= (1 - 1/√3)/(1 + 1/√3)

multiply by √3/√3

= (√3-1)/(√3+1)

but tan(-15) = -tan15

so

tan(-15°) = (1-√3)/(√3 + 1)

cos 3x cos 4x - sin 3x sine 4x

= cos(3x+4x) = cos 7x

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