Posted by **jeff** on Friday, May 28, 2010 at 9:23am.

I meant to type this one:

If the sine of an acute angle is 0.8, what is the sine of twice that angle?

1.60 or .64?

Thanks

- Algebra 2 -
**drwls**, Friday, May 28, 2010 at 11:15am
Neither. Sine can never exceed 1.

If the sine is 0.8, the cosine is 0.6.

(Think of a 3,4,5 right triangle, or use cos^2 = 1 - sin^2)

The sine is 2x is 2 sinx cosx.

In this case, that is 2*(3/5)(4/5)= 24/25

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