Domain and range of quadratic functions (video) | Khan Academy
https://www.khanacademy.org/math/algebra-home/alg-functions/alg-determining-the-range-of-a-function/v/domain-and-range-of-a-function-given-a-formula
WEBFor every polynomial function (such as quadratic functions for example), the domain is all real numbers. If f(x) = a(x-h)² + k , then if the parabola is opening upwards, i.e. a > 0 , the range is y ≥ k ; if the parabola is opening downwards, i.e. a < 0 , the range is y ≤ k .
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