a)x^2-...+1=(x-1)^2 =>x^2-2x+1 т.к (a-b)^2=a^2-2ab+b^2
b)...+6x+9=(2x+3)^2 =>4x^2+6x+9 т.к (a+b)^2=a^2+2ab+b^2
c)16a^2+...+25b^2=(4a+5b)^2=>16a^2+40ab+25b^2
