(1)a^4-a^3+a^2-a
=a^3(a-1)+a(a-1)
=(a-1)(a^3+a)
=a(a-1)(a^2+1)
(2)4a^2-9b^2+c^2-4ac
=(4a^2-4ac+c^2)-9b^2
=(2a-c)^2-(3b)^2
=(2a-c+3b)(2a-c-3b)
(3)(ax+by)^2+(bx-ay)^2
=(ax)^2+2abxy+(by)^2+(bx)^2-2abxy+(ay)^2
=(a^2+b^2)(x^2+y^2)
(1)a^4-a^3+a^2-a
=a^3(a-1)+a(a-1)
=(a-1)(a^3+a)
=a(a-1)(a^2+1)
(2)4a^2-9b^2+c^2-4ac
=(4a^2-4ac+c^2)-9b^2
=(2a-c)^2-(3b)^2
=(2a-c+3b)(2a-c-3b)
(3)(ax+by)^2+(bx-ay)^2
=(ax)^2+2abxy+(by)^2+(bx)^2-2abxy+(ay)^2
=(a^2+b^2)(x^2+y^2)