We'll manage the left side of the expression and we'll
            multiply the numerator and denominator by (1+sin x).
sqrt
            [(1+sin x)^2/(1-sin x)*(1+sin x)] = (1+sinx)/|cosx|
We'll
            recognize the difference of 2 squares at denominator:
sqrt
            [(1+sin x)^2/[1- (sin x)^2]
We'll apply the Pythagorean
            identity:
1- (sin x)^2 = (cos
            x)^2
sqrt [(1+sin x)^2/[1- (sin x)^2] = |(1+sin x)^2|/|cos
            x|
Since 1 + sin x >= 0 => |(1+sin x)| =
            (1+sin x)
sqrt [(1+sin x)^2/[1- (sin x)^2] = (1+sin x)/|cos
            x|
We notice that LHS = RHS, therefore the
            identity sqrt [(1+sin x)^2/[1- (sin x)^2] = (1+sin x)/|cos x| is
            verified.
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