Use derivatives to find the vertex of parabola y=x^2-4x+7?

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Wiggin42's profile pic

Wiggin42 | Student, Undergraduate | (Level 2) Valedictorian

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y=x^2-4x+7

Take the derivative:

y' = 2x - 4

Given that the original equation is concave up, we are looking for an absolute/local minimum. At a minimum, the slope is 0. So lets set the derivative equal to 0 and solve for x

0 = 2x - 4

x = 4/2 = 2. 

The vertex is at point x = 2. You can plug this back into the original to get the y value. 

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giorgiana1976 | College Teacher | (Level 3) Valedictorian

Posted on

The vertex of parabola represents an extreme point. In this case the parabola is convex and the vertex is it's minimum point.

Any extreme of a function can be determined using derivatives.

We'll determine f'(x) = y':

f'(x) = 2x - 4

We'll cancel f'(x):

2x - 4 = 0 => x - 2 = 0 => x = 2

The critical value of the function is x = 2. The extreme of the function will be calculated replacing x, into the expression of f(x), by the critical value found earlier.

f(2) = 2^2 - 4*2 + 7

f(2) = 4 - 8 + 7

f(2) = 3

The vertex of parabola is represented by the pair of coordinates: (2 , 3).

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