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Unformatted text preview:μ = EX = xf ( x ) dx . The second moment E ( X 2 ) = x 2 f ( x ) dx . The variance σ 2 = E ( X 2 )-μ 2 . Partial derivatives. Given f ( x, y ), ∂f ∂x is computed by holding y constant and differentiat-ing the resulting function of x . Higher order partial derivatives such as ∂ 2 f ∂x∂y are computed by first taking the partial dervia-tive with respect to y , then taking the partial derivative of the result with respect of x . Useful derivative formulas. d dx g ( f ) = g ( f ) f d dx fg = f g + fg d dx f g = f g-fg g 2