Exercise algebra.equations.quadratic.no-abc

Description
solve a quadratic equation without abc-formula

Derivation

40-4*x^2 == -4*x^2-20*x

⇒ algebra.equations.quadratic.cancel

40 == -20*x

⇒ algebra.equations.coverup.times

-2 == x

⇒ algebra.equations.linear.flip

x == -2