y=(a^x + c)^(-1/x)=e^[ln(a^x + c)^(-1/x)]=e^{(-1/x)[ln(a^x + c)]}dy/dx=e^{(-1/x)[ln(a^x + c)]}×d{(-1/x)[ln(a^x + c)]}/dx=[(a^x + c)^(-1/x)]×{[ln(a^x + c)]/x²-(a^x)lna/[x(a^x + c)]}