Exercise algebra.equations.quadratic.no-abc

Description
solve a quadratic equation without abc-formula

Derivation

20-2*x^2 == -2*x^2-10*x

⇒ algebra.equations.quadratic.cancel

20 == -10*x

⇒ algebra.equations.coverup.times

-2 == x

⇒ algebra.equations.linear.flip

x == -2