4x^2+2x-9y^2-3y
=(2x)²+2x+(1/2)²-[(3y)²+3y+(1/2)²]
=(2x+1/2)²-(3y+1/2)²
=(2x+1/2+3y+1/2)(2x+1/2-3y-1/2)
=(2x+3y+1)(2x-3y)