User:HannsEwald/sandbox

$K={\frac {RT-S^{2}}{\left(1+P^{2}+Q^{2}\right)^{2}}}$

Failed to parse (syntax error): {\displaystyle K = \frac{RT−S^2}{(1+P^2+Q^2)^2}}

Original from Differential geometry of surfaces

Failed to parse (syntax error): {\displaystyle K = \frac{(RT − S^2)}{\left (1 + P^2 + Q^2\right )^2}}