2x^2-5x-2
=2(x^2-5x/2)-2
=2(x^2-5x/2+25/16)-50/16-2
=2(x-5/4)^2-82/16
=2[(x-5/4)^2-41/16]
=2(x-5/4-√41/4)(x-5/4+√41/4)