Writing a quadratic equation from a graph

[crod]

Your method of finding a doesn’t always work. It’s a quadratic function so the slope changes depending on where you are on the function. For the first example, you could have chosen the point (-1, 5) as your second point, in which case you would assume a = -2. Instead, It’s best to plug in the second point for (x, y) and solve for a.

[alexmccall]

The solution to the last problem is incorrect and a 2/2 a-value gives an 'concave up' parabola, quite clearly. You must surely mean the a-value is "down - 2 and across +4", giving an a-value of -1/2 and the solution is thus -1/2(x-2)^2.

[leonhardeuler]

The second parabola is the exact same problem of my homework lol

[ThirteenStrings]

This is straight up wrong. Math teacher here looking for a help video for a student. Please take this down so you don't confuse any more students. Your first example is okay but the second one is not correct and will lead to misconceptions. Not only did you forget to make the a value negative but it's clear to see if you plug x=4 into your equation you get 4 not -2 as you should.

[biswanathbera]

Solution is not correct. Here a=-1/2 not -1. So the equation shoud be y=-1/2(x-2) ^2, I think.

[celsoseno]

I don't understand how to get the a

[saminouri]

The "C" value is the value of "y" where the graph intersepts the "y" axis.please make sure you teach everything right.

[jerrywang]

It is actually +k, c and k are totally different values.

[patrickober]

my vertex isnt on a specific point in the graph what do i do

[sudikris]

What is a and why is it the missing value

[caleblawrence]

Why are youtubers better than real teachers