y ≥ 2 or [2, +∞)
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Given function:
This is a quadratic function in standard form.
Let's convert it into vertex form by completing the square:
- f(x) =
- x² + 2x + 3 =
- x² + 2x + 1 + 2 =
- (x + 1)² + 2
From the final expression we see it is a parabola that opens up (since leading coefficient is positive) and with minimum value at vertex, f(x) = 2, when x = - 1.
So its range is any value greater or equal to 2: