* Can someone please help me??? * * 8th-grade math * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 answers:
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We have
and
So
and
So
We have to find the parameter a so that (-1,2) is part of the function f(x) = ax²+4.
To check if a point is part of a function, we can replace the values of x and y = f(x) with the coordinates of the point and then, if the equation stays true, then the point is part of the function.
So for (x,y) = (-1,2) to be part of the function y = f(x), this equation has to stands true:
Then, the function would have to be f(x) = -2x² + 4.
We can check with a graph as:
Answer: a = -2
Check the picture below.
notice, the focus point is at 4,5 whilst the directrix line is at y = -3, below the focus point, meaning the parabola is vertical and opening upwards.
keeping in mind that the vertex is "p" distance from either of these fellows, then the vertex is half-way between both of them, notice in the picture, the distance from y = 5 to y = -3 is 8 units, half that is 4 units, thus the vertex 4 units from the focus or 4 units from the directrix, that puts it at (4,1), whilst "p" is 4, since the parabola is opening upwards, is a positive 4 then.
notice, the focus point is at 4,5 whilst the directrix line is at y = -3, below the focus point, meaning the parabola is vertical and opening upwards.
keeping in mind that the vertex is "p" distance from either of these fellows, then the vertex is half-way between both of them, notice in the picture, the distance from y = 5 to y = -3 is 8 units, half that is 4 units, thus the vertex 4 units from the focus or 4 units from the directrix, that puts it at (4,1), whilst "p" is 4, since the parabola is opening upwards, is a positive 4 then.