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一、已知三点求二次函数的解析式已知二次函数的图象经过三个已知点或变相已知三点坐标时,把这三点的坐标代入一般式y=ax~2+bx+c中,可得以a、b、c为未知数的三元一次方程组,解此方程组求得a、b、c的值,再代入一般式可得所求函数解析式.例1已知二次函数的图象经过A(-1,3)、B(1,3)、C(2,6)三点,求其解析式.解设这个二次函数的解析式为y=ax~2+bx+c,
First, the known three-point quadratic function of the analytical known quadratic function of the image after three known points or known three-point coordinates in disguise, the coordinates of these three points into the general formula y = ax ~ 2 + bx + c, we can get a, b, c for the unknowns of the ternary system of equations, the solution of this system to obtain the value of a, b, c, and then substituted into the general can find the function analytic formula. It is known that the image of the quadratic function is solved by three points of A (-1,3), B (1,3) and C (2,6), and the analytical solution of this quadratic function is y = ax ~ 2 + bx + c,