Write as (a^2+b^2-c^2)^2-4a^2b^2
color(white)(-)a^2(a^2+b^2-c^2) =a^4+a^2b^2-a^2c^2
color(white)(-)b^2(a^2+b^2-c^2)= 0color(white)(.)+a^2b^2""+color(white)(.)0color(white)(.)-b^2c^2+b^4
-c^2(a^2+b^2-c^2) = ul(color(white)(.)0color(white)(.)+color(white)(.)0color(white)(.) -a^2c^2-b^2c^2+0+c^4)" Add"
" "a^4+2a^2b^2 -2a^2c^2-2b^2c^2+b^4+c^4
Now add the other part:
" "a^4+2a^2b^2 -2a^2c^2-2b^2c^2+b^4+c^4
" "ul(" "-4a^2b^2" ")
" "a^4-2a^2b^2-2a^2c^2-2b^2c^2+b^4+c^4