Question

What is the vertex of the parabola whose equation is y = (x + 1)2 + 3? (-1, -3) (-1, 3) (1, 3)

Answer 1

Algebra:
A standard parabola is y = x^2. Its vertex is at (0,0)
You can change the position (or vertex) of the parabola.
To move a parabola across the x-axis, you can add or subtract a number from x WITHIN brackets of the ^2
eg. (x + 1)^2 will move the parabola across the x-axis. It will move is one unit to the LEFT (as the sign is opposite to the direction it moves ie. The sign it + but you move the whole parabola in the -ve direction).
Adding or subtracting a number from x OUTSIDE of the ^2 moves the parabola up or down the y-axis
eg. x^2 + 3 will move the parabola UP 3 units (the sign is the same as the direction it moves when the added/subtracted number is outside of the ^2 ie. the sign is positive so the parabola moves up in the positive direction)

From this, we can conclude that because (x + 1)^2 + 3, the vertex will be where x = -1 and where y = 3

Vertex : (-1,3)



Calculus:
f(x) = (x + 1)^2 + 3 = x^2 + 2x + 1 + 3 = x^2 + 2x + 4
Expanding the formular to make it easier to differentiate

f'(x) = 2x + 2
Differentiating (finding the formular the the gradiet of the parabola)

0 = 2x + 2
When the gradient is equal to zero, it must be the vertex

-2 = 2x
-2/2 = x
x = -1
Solve to give the x value at the vertex

f(x) = (x + 1)^2 + 3
= (-1 + 1)^2 + 3
Substitute x = -1 into original equatiom to find y value at the vertex

= (0)^2 + 3
= 0 + 3
= 3
Solve for y

Vertex : (-1,3)