Solve the Quadratic Inequality: y = -1/7x^2 - 23/7x > 0

Question

Look at the following function:

y=17x2237x y=-\frac{1}{7}x^2-2\frac{3}{7}x

Determine for which values of x x the following is true:

f(x) > 0

Step-by-Step Solution

First, we need to find the roots of the quadratic equation:

The quadratic is given by:
y=17x2177x y = -\frac{1}{7}x^2 - \frac{17}{7}x

Setting y=0 y = 0 to find the x x -intercepts (roots):
17x2177x=0-\frac{1}{7}x^2 - \frac{17}{7}x = 0

Factor out the common factor, 17x-\frac{1}{7}x:
17x(x+17)=0-\frac{1}{7}x(x + 17) = 0

This gives the roots:
x=0 x = 0 and x+17=0x=17 x + 17 = 0 \rightarrow x = -17

These roots divide the number line into intervals. We need to determine where y>0 y > 0 . Because the coefficient of x2 x^2 is negative, the parabola opens downward. The function will be positive between the roots.

Thus, we test the interval:
(17,0)(-17, 0)

Since the parabola opens downward, the function y>0 y > 0 is true in the interval 17<x<0 -17 < x < 0 .

Therefore, the solution to the problem is 17<x<0-17 < x < 0, which corresponds to choice 3.

Answer

-17 < x < 0