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An equation of the line tangent to y=x^3+3x^2+2 at its point of inflection is

Monica build a remote control toy airplane for science project to test the plane she launched it from the top of a building the plane travel a horizontal distance of 50 feet before landing on the ground a quadratic function which models the height of the plane in feet relative to the ground at a horizontal distance of x feet from the building is shown

Find the domain of the following expression: 1/(√x)-2