20x^2+180/x-170=(20x^3-170x+180)/x. The zeroes are found by solving 20x^3-170x+180=0 or 10(2x^3-17x+18)=0.
When x=2 the expression is zero so we divide by this zero:
2 | 2 0 -17 18
2 4 8 -18
2 4 -9 | 0 = 2x^2+4x-9. This quadratic has zeroes x=(-4±√(16+72)/4=1.3452, -3.3452.
Therefore the zeroes are 2, 1.3452, -3.3452