Answer:
The vertex point of the function is (4 , -25)
Explanation:
- Lets explain how to find the vertex of the quadratic function
- The form of the quadratic function is f(x) = ax² + bx + c , where
a , b , c are constant
# a is the coefficient of x²
# b is the coefficient of x
# c is the y-intercept (numerical term)
- The x-coordinate of the vertex point is -b/a
- The y-coordinate of the vertex point is f(-b/a)
* Lets solve the problem
∵ f(x) = x² - 8x - 9
∴ a = 1 , b = -8 , c = -9
∵ The x-coordinate of the vertex point is -b/a
∴ The x-coordinate of the vertex point = -(-8)/2(1) = 8/2 = 4
- To find the y-coordinate of the vertex point substitute x by 4 in f(x)
∵ f(4) = (4)² - 8(4) - 9
∴ f(4) = 16 - 32 - 9
∴ f(4) = -25
∵ f(4) is the y-coordinate of the vertex point
∴ The y-coordinate of the vertex point is -25
∴ The vertex point of the function is (4 , -25)