Question

The graph of $y = ax^2 + bx + c$ is shown below. Find $a \cdot b \cdot c$. (The distance between the grid lines is one unit.)

Answer 1

Answer:

$a\cdot b\cdot c=\frac{15}{4}$

Step-by-step explanation:

Vertex is the minimum or maximum point of parabola

Vertex of parabola is (h,k)

Therefore, from given graph (-3,-2) is the lowest point.

Vertex of parabola is at (-3,-2).

Standard equation of parabola

$y-k=a(x-h)^2$

Substitute the values

$y-(-2)=a(x-(-3))^2=a(x+3)^2$

$y+2=a(x+3)^2$

(-1,0) lies on the parabola.

Therefore, it satisfied the equation of parabola.

$0+2=a(-1+3)^2=4a$

$a=2/4=1/2$

Now, using the value of a

$y+2=1/2(x+3)^2=1/2(x^2+6x+9)$

$y+2=\frac{1}{2}x^2+3x+\frac{9}{2}$

$y=\frac{1}{2}x^2+3x+\frac{9}{2}-2$

$y=\frac{1}{2}x^2+3x+\frac{9-4}{2}$

$y=\frac{1}{2}x^2+3x+\frac{5}{2}$

By comparing with

$y=ax^2+bx+c$

We get

$a=\frac{1}{2}, b=3, c=5/2$

$a\cdot b\cdot c=\frac{1}{2}\times 3\times \frac{5}{2}$

$a\cdot b\cdot c=\frac{15}{4}$