\(\dfrac{213^2-26\cdot213+13^2}{311^2-111^2}\)
\(=\dfrac{213^2-2\cdot213\cdot13+13^2}{\left(311-111\right)\left(311+111\right)}\)
\(=\dfrac{200^2}{200\cdot422}=\dfrac{200}{422}=\dfrac{100}{211}\)
\(129^2+29^2-58\cdot129\)
\(=129^2-2\cdot129\cdot29+29^2\)
\(=\left(129-29\right)^2=100^2=10000\)