1) b^4+4b^2-5 = (b^2)^2+2*b^2*2+2^2-2^2-5 = (b^2+2)^2-4-5 = (b^2+2)^2-9

2) a^2-6a+5 = a^2-2*a*3+3^2-3^2+5 = (a-3)^2-9+5 = (a-3)^2-4