Angles measured in degrees.
If with positive integers and is not a prime, find .
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Lets first make everything into radians,
s = ∏ k = 1 4 5 ( c s c 2 ( 2 k − 1 ) 1 8 0 π + 3 )
s = ∏ k = 1 4 5 ( c o t 2 ( 2 k − 1 ) 1 8 0 π + 4 )
If we find a polynomial p(x) whose roots are c o t 2 ( ( 2 k − 1 ) 1 8 0 π ) all we have to do then is find p(-4).
The expression for tan(nx) is as follows
t a n ( n x ) = 1 − ( n 2 ) t a n 2 ( x ) + ( n 4 ) t a n 4 ( x ) − . . ( n 1 ) t a n ( x ) − ( n 3 ) t a n 3 ( x ) + . .
This expression can be obtained quite easily using complex no.s
We observe that for all θ = ( 2 k − 1 ) π / 1 8 0
t a n ( 9 0 θ ) = t a n ( ( 2 k − 1 ) π / 2 )
which is undefined
This implies that for these values of θ the denominator for the expression of t a n ( 9 0 θ ) = 0
So we've got a polynomial in t a n ( θ ) whose roots are t a n ( ( 2 k − 1 ) π / 1 8 0 ) ,
p ( t a n θ ) = ( 9 0 0 ) t a n 0 ( θ ) − ( 9 0 2 ) t a n 2 ( θ ) + ( 9 0 4 ) t a n 4 ( θ ) + . . .
or p ( c o t θ ) = ( 9 0 0 ) c o t 9 0 ( θ ) − ( 9 0 2 ) c o t 8 8 ( θ ) + ( 9 0 4 ) c o t 8 6 ( θ ) + . .
or p ( c o t 2 θ ) = ( 9 0 0 ) c o t 2 ( θ ) 4 5 − ( 9 0 2 ) c o t 2 ( θ ) 4 4 + ( 9 0 4 ) c o t 2 ( θ ) 4 3 + . .
Putting x= c o t 2 ( θ ) ,we get p ( x ) = x 4 5 − ( 9 0 2 ) x 4 4 + ( 9 0 4 ) x 4 3 = ∏ k = 1 4 5 ( x − c o t 2 ( ( 2 k − 1 ) π / 1 8 0 ) )
Putting x = − 4 ,we get
s = ∑ r = 1 4 5 ( 9 0 2 r ) 2 2 r
= 2 3 9 0 + 1
Hence 2 s − 1 = 3 9 0 = 9 4 5
m = 9 , n = 5