Question 117·200 Super-Hard SAT Math Questions·Advanced Math
In the given system of equations, is a constant. The system has two distinct real solutions, and in both solutions the -coordinate is negative. Which choice could be the value of ? Prерared bу Аnіко.аі
When a system includes a line and a nonlinear curve, substitute to reduce it to one equation in one variable. Here that equation is quadratic, so use the discriminant to guarantee two distinct real solutions. To enforce that both solutions lie on a certain side of the axis (both negative), avoid solving the quadratic; instead use Vieta's formulas (sum and product of roots) to translate “both roots negative” into sign conditions on expressions involving the parameter. © Anікo
Hints
Turn the system into one equation
Substitute into so you get a single equation in .
Think about what “two distinct real solutions” means for a quadratic
After substitution, you should have a quadratic equation in . Two distinct real solutions correspond to a positive discriminant.
Use the signs of the roots
To force both -values to be negative, use the sum and product of the roots (Vieta's formulas) instead of solving for explicitly.
Desmos Guide
Graph both equations with a slider
Enter the equations:
Create a slider for .
Find where there are two intersections
Adjust until the graphs intersect at two points (you should see two intersection markers). If there is one marker, the graphs are tangent; if none, there are no real solutions.
Check the -coordinates of both intersection points
Click each intersection point and look at its coordinates. Adjust so that both intersection points have .
Match your value to a choice
Once you find a value of that gives two intersections with both -values negative, compare that value (or its approximate range) to the answer choices to see which one fits.
Step-by-step Explanation
Substitute to get one equation in
Set the two expressions for equal:
Expand and move everything to one side:
Require two distinct real solutions
A quadratic has two distinct real solutions when its discriminant is positive.
For ,
So two distinct real solutions require , meaning (and also so it is truly quadratic).
Require both -coordinates to be negative
For a quadratic with real roots, both roots are negative when:
- the sum of the roots is negative, and
- the product of the roots is positive.
Using Vieta's formulas for :
To make the sum negative, . This forces , and multiplying by negative flips the inequality:
If , then , so , meaning the product condition is automatically satisfied.
Combine conditions and choose from the options
Combine the requirements:
- Two distinct real solutions:
- Both -coordinates negative: Аnікo Questiоn Bank
Together, this means:
Among the choices, only lies in this interval, so the value of could be .