Estonian Math Competitions

Transforming the l.h.s. of the equation gives $$\begin{array}{rl}2a(c-a)-b(2a+b)+c(2b-c)& =2ac-2a^2-2ab-b^2+2bc-c^2\\ & =-a^2-(a+b-c{)}^2.\end{array}$$ The equality $-a^2-(a+b-c{)}^2=2020$ cannot be valid since all terms of its l.h.s. are non-positive whereas the r.h.s. is positive.