Question

What is the vertex of the graph of the function f(x) = x2 − 4x?

Answer 1

Answer:

(2, -4).

Step-by-step explanation:

x^2 - 4x

= (x - 2)^2 - 4.

So the vertex is at

(2, -4).

Answer 2

Answer:

(2,-4)

Step-by-step explanation:

x²-4x

First, we need to complete the square of this quadratic.

1) Half the coefficient of x and subtract it (depends on the sign) from x. Then, square the whole expression.

(x-2)²

2) If this was to be expanded as a double bracket, we would acquire:

x²-4x+4

In order to achieve the form above, we need to subtract 4. This can be found quickly by subtracting the square of the integer from the bracket. (Ignore the sign when squaring here.)

(x-2)²-4           ------>This is in the completing the square from.

From this, the vertex is determined by using the opposite sign of the number in the bracket for the $x$ coordinate and the outside number is kept constant for the $y$. Note that, in graph transformations, the number inside the brackets is the "opposite of what you expect"; the same logic is applied here.

Therefore, the vertex is (2,-4)