The expression x4 + x2 + 1 can not be factored using known techniques. However, if x2 is added and subtracted from the expression, the resulting expression can be factored: 4 = x4+ 2x2+1 - 22 = (a2 + 1)2 - 22 = (x2 + 2+1) (202 - 2 + 1) Use this to factor x4 + 5x2 + 9 O a ) ( x 2 + x+ 3)(x2 - x+ 3) O b ) ( x 2 + x - 3) ( x 2 - x - 3) O c) ( x 2 - x - 3) (x 2 - x + 3) O d) ( x 2 + x + 3) ( x 2 + x+ 3)