Solve the following equation by making an appropriate substitution. x Superscript negative 2 Baseline minus 2 x Superscript negative 1 Baseline minus 15 equals 0 Make an appropriate substitution and rewrite the equation in quadratic form. Let uequals xz-1 x Superscript negative 1​, then the quadratic equation in u is u^2-2u-15(-5)(u+3) (u-5 )(u+3 ).