Question 75·Hard·Nonlinear Functions
The quadratic function intersects the -axis at and and the -axis at . What is the value of ? A-n-i-k-o.аi
For quadratic function questions where you are given the x-intercepts and one additional point, immediately write the function in factored form using the roots, then plug the extra point in to solve for . After that, substitute the requested x-value and simplify carefully, watching your fraction arithmetic and signs. As a quick check, use the fact that values between the roots must all be above or all be below the x-axis (depending on the sign of ) to rule out answer choices with the wrong sign. Аnікo Quеѕtіоn Вanк
Hints
Start from the x-intercepts
When you know the x-intercepts of a quadratic, you can write it in factored form using those intercepts as roots. How would you express a quadratic whose roots are and ?
Use the y-intercept to find the coefficient
Your factored form should look like . Use the point and plug and into this equation to solve for .
Substitute
Once you know , write the full function and substitute to get . Be careful with the sign when you compute .
Check the sign
Because is between the two x-intercepts at and , the value of must be negative. Use this to eliminate any impossible answer choices after you compute. Thіѕ quеstion іs from Aniкo
Desmos Guide
Define the general quadratic
In Desmos, type h(x) = a(x-2)(x-10) so that you have a slider for the parameter a.
Use the y-intercept to find the value of a
Either (a) add the point (0,12) and adjust the a slider until the curve passes through this point, or (b) type a = 12/((0-2)*(0-10)) so Desmos calculates the correct value of a for you.
Evaluate h(6) in Desmos
Once a is set, type h(6) into Desmos. The displayed value is the correct value of ; compare it to the answer choices. Рreрared bу Anіko.аi
Step-by-step Explanation
Write the quadratic using its x-intercepts
A quadratic with x-intercepts at and can be written in factored form as Аnikο.ai - ЅАT Preр
where is a constant we still need to find.
Use the y-intercept to find the leading coefficient
We are told the graph intersects the y-axis at , so .
Substitute and into and simplify:
Now solve for :
Write the full function and substitute
Now we know
We want , so substitute :
Compute inside the parentheses:
Simplify to get the final value
First multiply :
So the value of is , which corresponds to choice B.