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Some Decic Sin and Cos Sum to Rational Numbers (Posted on 2023-07-12) Difficulty: 3 of 5
Solve for x:
sin10(x)+cos10(x) = 61/256
where, x is in radians.

See The Solution Submitted by K Sengupta    
Rating: 5.0000 (1 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re: what I find Overlooked | Comment 2 of 5 |
(In reply to what I find by Charlie)

I don't have an analytic solution, but there there's a bit that can teased out of your findings.  Some of those 'complex'  solutions have imaginary parts that are suspiciously small.

Take the 7th one on the list: -2.61799387799149 +  5.55111512312578e-17i
Maybe this is just -5pi/6
sin(-5pi/6)=-1/2
cos(-5pi/6)=-sqrt(3)/2
sin(-5pi/6)^10+cos(-5pi/6)^10=1/1024+243/1024=244/1024=61/256
So, they are just real solutions with period pi/2:

pi/6+n*pi/2, pi/3+n*pi/2, 

You can also see the real parts of many pairs that are indeed complex sum to pi.

  Posted by Jer on 2023-07-12 16:15:33
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