∴ f (x) = sin2x-sinxcosx-sinxcosx+3cos2x = 2+radical 2sin(-2x+π/4)

2-radical number 2

(2) Regarding the symmetry of the origin ∴-2(x+a)+π/4=-2x ∴2a=π/4∴a=π/8, so d=(-π/8, -2) has the shortest length.