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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
cos(65) = 5/x // - 5/x
cos(65)-(5/x) = 0
cos(65)-5*x^-1 = 0
-5*x^-1 = -cos(65) // : -5
x^-1 = cos(65)/5
-1 < 0
1/(x^1) = cos(65)/5 // * x^1
1 = (cos(65)/5)*x^1 // : cos(65)/5
5*(cos(65))^-1 = x^1
x = 5*(cos(65))^-1
x = 5*(cos(65))^-1
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