Question 230·Medium·Nonlinear Equations in One Variable; Systems in Two Variables
Which of the following ordered pairs satisfies the system below?
For systems where one equation is linear and the other is nonlinear, a fast approach is to solve the linear equation for one variable and substitute into the other, reducing the system to a single-variable equation you can factor or solve with the quadratic formula. On multiple-choice questions, you can also quickly test each answer by substituting into both equations—eliminate any pair that fails even one equation and remember that the correct ordered pair must make both equations true.
Hints
Start with the simpler equation
Look at . Can you solve this equation for (or for ) in terms of the other variable?
Use substitution
Once you have written in terms of , substitute that expression into the other equation so that the new equation has only in it.
Solve and then match to choices
After you solve the resulting equation for , use to find the corresponding -values. Then see which of the answer choices match the pair(s) you found.
Alternatively, test answer choices
For each answer choice, plug and into both equations and check whether both are true. Only one ordered pair will make both equations true at the same time.
Desmos Guide
Graph both equations in Desmos
Rewrite each equation in the form :
- From , get .
- From , get . In Desmos, enter y = 5 - x and y = x^2 - 7 as two separate graphs.
Find the intersection that matches an answer choice
Look at the point(s) where the line and the parabola intersect. Hover or tap on each intersection to see its coordinates, then choose the answer option whose ordered pair exactly matches one of those intersection points.
Step-by-step Explanation
Use the linear equation to express one variable
From the first equation,
solve for :
Now you can replace in the second equation with .
Substitute into the second equation and simplify
Substitute into the second equation :
Distribute the minus sign:
Move all terms to one side:
Now solve this quadratic.
Solve the quadratic for x and find corresponding y values
Factor the quadratic:
So the possible -values are
Use to find each corresponding :
- If , then .
- If , then .
So the system has two solutions: and .
Match the solution to the answer choices
Compare the solution pairs and to the answer options:
- (2, 3)
- (-4, 2)
- (4, 1)
- (3, 2)
Only appears in the list, so the ordered pair that satisfies the system is .