`a. = (a^2+b^2-5)^2-[2(ab+2)]^2`
`= [(a^2+b^2-5)-2(ab+2)][(a^2+b^2-5)+2(ab+2)]`
`= [a^2+b^2-5-2ab-4][a^2+b^2-5+2ab+4]`
`= [(a-b)^2-9][(a+b)^2-1]`
`= [(a-b)^2-3^2][(a+b)^2-1^2]`
`= (a-b-3)(a-b+3)(a+b-1)(a+b+1)`
`b. = [2bc-(b^2+c^2-a^2)][2bc+(b^2+c^2-a^2)]`
`= [2bc-b^2-c^2+a^2][2bc+b^2+c^2-a^2]`
`= [a^2-(b^2-2bc+c^2)][(b+c)^2-a^2]`
`= [a^2-(b-c)^2](b+c-a)(b+c+a)`
`= (a-b+c)(a+b-c)(b+c-a)(b+c+a)`