Question 43·Easy·Nonlinear Equations in One Variable; Systems in Two Variables
Consider the system of equations
Which ordered pair satisfies both equations?
For systems where one equation is linear and the other is nonlinear (like a circle), substitution is usually the fastest method: solve the linear equation for one variable, substitute into the nonlinear equation, and solve the resulting quadratic. Then, use the linear equation to find the corresponding other coordinate and quickly check which resulting ordered pair appears in the choices and satisfies both original equations. If time is short, you can also plug in answer choices directly, testing each pair in both equations and eliminating those that fail either one.
Hints
Choose which equation to start from
One equation is already solved for . How can you use to rewrite the other equation so that it has only in it?
Substitute and simplify
Replace with in . After substituting, carefully expand and combine like terms.
Solve the quadratic equation
Once you have a quadratic equation in , try to factor it. What two numbers multiply to give the constant term and add to give the coefficient of ?
Match your solutions to the choices
Use to find for each you found. Then check which of the resulting ordered pairs appears in the answer choices and still satisfies .
Desmos Guide
Graph the circle
In Desmos, enter the equation x^2 + y^2 = 25. This will graph the circle of radius 5 centered at the origin.
Graph the line
On a new line in Desmos, enter y = x - 1. This will graph the straight line that might intersect the circle at up to two points.
Find the intersection points and compare
Click or tap on each point where the line and circle intersect; Desmos will display the coordinates of these intersection points. Compare those coordinates to the answer choices and select the option whose ordered pair matches one of the intersection points.
Step-by-step Explanation
Use the linear equation to substitute
From the second equation, we know .
Substitute into the first equation so that the equation has only in it.
Write and simplify the equation in one variable
After substitution, the first equation becomes
Now expand and combine like terms:
So
Divide both sides by to simplify:
Solve the quadratic for x
Factor the quadratic equation:
So the possible -values are
Find the corresponding y-values and match to a choice
Use to find for each :
- If , then , giving the point .
- If , then , giving the point .
Both points satisfy the original circle equation, but only one of them appears in the answer choices. The ordered pair that satisfies both equations and is listed among the options is .