Key idea: Geometric meaning of zeros
Zeros of p(x) are exactly the **x-coordinates where the graph y=p(x) meets the x-axis**.
- **Linear** y = ax + b: graph is a straight line, crosses x-axis ONCE → exactly 1 zero.
- **Quadratic** y=ax2+bx+c: graph is a parabola. Possible cases:
- Crosses x-axis at 2 points → 2 distinct real zeros.
- Touches x-axis at 1 point → 1 repeated zero (vertex on x-axis).
- Does not meet x-axis → no real zeros.
- **Cubic** y=ax3 + …: shape is a curve that crosses 1, 2, or 3 times → 1, 2, or 3 real zeros.
So 'find the zeros' is the algebraic version of 'find where the graph crosses the x-axis'.