Answer:
1a. -( x + 1)² + 4
1b. y-intercept at y = 3
1c. x-intercepts at x = -3 and x = 1
Derivation of 1b and 1c below
Step-by-step explanation:
Question 1a
The vertex equation form of a parabola is given by
y = a(x-h)² + k where (h, k) are the coordinates of the vertex
If a > 0 then the parabola is facing up(vertex is at a minimum) and if a < 0 then parabola is facing down (vertex at a maximum)
From the graph we see that the parabola is facing down so a = -1
The vertex is at (-1, 4) so h = -1 and k = 4
Therefore the equation of the parabola is
y = -1(x - h)² + k = -1(x- (-1))² + 4 = -1(x + 1)² + 4
y = -( x + 1)² + 4 (Answer 1a)
Question 1b
The y-intercept is the y-value where the parabola crosses the y-axis. From the graph we see that the parabola crosses the y-axis at y = 3 and x = 0
So y-intercept from the graph is 3
To solve algebraically, set x = 0 in the parabola equation and solve for y
We get, for x = 0,
y = - (0 + 1)² + 4
y = -(1²) + 4 = -1 + 4 = 3
Hence verified
Question 1c
There will be two x-intercepts for a parabola. Looking at the graph we see that the parabola intersects the x-axis at two points (-3, 0) and (1, 0). So the two x-intercepts are -3 and 1
Algebraically we can determine the x-intercepts by setting y = 0 and solving for the two values of x
Setting y = 0 in the parabolic equation, we get
y = 0 = -(x + 1)² + 4
Switch sides
-(x + 1)² + 4 = 0
-(x + 1)² = -(x² + 2x + 1) = -x² -2x - 1
-(x + 1)² + 4 = 0
==> -x² -2x - 1 + 4 = 0
==> -x² - 2x +3 = 0
Multiply by -1 both sides
==> x² + 2x - 3 = 0
Solve this quadratic equation by factoring
x² + 2x - 3 = (x - 1)(x + 3) = 0
The solutions are
x - 1 = 0 ==> x = 1
x + 3 = 0 ==> x = -3
Hence verified
