Question 123·200 Super-Hard SAT Math Questions·Advanced Math
is a quadratic function. In the -plane, the graphs of and intersect at the points whose -coordinates are and .
If , which choice is the value of ?
When a quadratic intersects a known function at two -values, subtract the functions. The difference is a quadratic that equals at those -values, so it must have factors for those roots: . Then use the extra point to find and evaluate at the requested . From aniкο.ai
Hints
Use what it means to intersect
If two graphs intersect at a given -value, then the two -values are equal at that -value.
Look at a difference of functions
Consider the function . What do you know about its value at and at ?
Write a quadratic with given zeros
A quadratic with zeros at and can be written as for some constant .
Desmos Guide
Enter a quadratic model using the intersection points
Enter
y = 2x + 1 + a(x+1)(x-5)
where is a slider.
Use the point to determine
On a new line, enter the point (2,7).
Adjust the slider until the curve passes through (2,7) (so the point lies on the graph).
Create a table to read
Create a table for the function and enter in the table.
Interpret the table output
Read the corresponding -value in the table; that value is .
Step-by-step Explanation
Express the difference using the intersection information
Since and , the function Anikо АІ Тutor
is a quadratic with zeros at and . So for some constant ,
Use the given point to find
Substitute and :
So , and therefore .
Evaluate
Now substitute :
State the answer
Therefore, , so the correct choice is .