Question #273

Find the general form of the solutions of the equation x such that sin x = cos 5x
Example: for the equation tanx=1, the solutions can be described by x = pi/4 + n*pi, n is an integer.

Expert's answer

sin x = cos5x

sin x = cos(pi/2 - x)

cos(pi/2 - x) = cos(5x)

cos(pi/2 - x) - cos(5x) = 0

-2sin(( pi/2-x+5x)/2 ) sin ((pi/2-x-5x)/2)=0

-2sin (pi/4+2x) sin (pi/4 -3x)= 0

х=pi*n/2-pi/8 or х=pi/12-pi*n/3, nEZ

sin x = cos(pi/2 - x)

cos(pi/2 - x) = cos(5x)

cos(pi/2 - x) - cos(5x) = 0

-2sin(( pi/2-x+5x)/2 ) sin ((pi/2-x-5x)/2)=0

-2sin (pi/4+2x) sin (pi/4 -3x)= 0

х=pi*n/2-pi/8 or х=pi/12-pi*n/3, nEZ

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