$\begin{array}{l} a) (a^2+b^2-c^2)-(a^2-b^2+c^2)^2\\\Leftrightarrow a^{2}+b^{2}-c^{2}-(a^{4}+b^{4}+c^{4}-2a^{2}b^{2}+2a^{2}c^{2}-2b^{2}c^{2})\\\Leftrightarrow a^{2}+b^{2}-c^{2}-a^{4}-b^{4}-c^{4}+2a^{2}b^{2}-2a^{2}c^{2}+2b^{2}c^{2}\\b) (a+b+c)^2+(a+b-c)^2-2.(a+b)^2\\\Leftrightarrow a^{2}+b^{2}+c^{2}+2ab+2ac+2bc+a^{2}+b^{2}+c^{2}+2ab-2ac-2bc-2(a^{2}+2ab+b^{2})\\\Leftrightarrow a^{2}+b^{2}+c^{2}+2ab+a^{2}+b^{2}+c^{2}+2ab-2a^{2}-4ab-2b^{2}\\\Leftrightarrow 0+0+2c^{2}+0\\\Leftrightarrow 2c^{2}\\c) (a+b+c)^2+(a-b+c)^2+(a+b-c)^2+(b+c-a)^2\\\Leftrightarrow a^{2}+b^{2}+c^{2}+2ab+2ac+2bc+a^{2}+b^{2}+c^{2}-2ab+2ac-2bc+a^{2}+b^{2}+c^{2}+2ab-2ac-2bc+a^{2}+b^{2}+c^{2}+2bc-2ab-2ac\\\Leftrightarrow 4a^{2}+4b^{2}+4c^{2}\end{array}$

a , (a²+b²- c)²-(a²- b²+c²)²

=    a²+b²-c²-a²+b²- c²

= a⁴+b⁴-c⁴ 

b , (a+b+c²)+(a+b-c)²-2 . ( a+b)²

     = a²+b²+c²+a²+b²-c²-2 . a²+b² 

      = a⁶+b⁶-c⁶- 2 

bn xem đúng ko nha mình tí nữa làm nốt bây giờ có việc