Rút gọn phân số 21/42 ta được phân số tối giản là

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 center and the radius of the circle with the equation: x^2-2x+y^2+4y+1=0?

Which of the following parabolas opens down?