Question 208·Hard·Nonlinear Equations in One Variable; Systems in Two Variables
Which ordered pair is a solution to the system of equations above?
When one equation in a system is linear (like ) and the other is nonlinear (like ), the fastest reliable method is substitution: replace in the nonlinear equation with the linear expression, simplify to a quadratic in one variable, and solve using the quadratic formula. Then, for each -value you find, plug back into the linear equation to get the matching and compare directly with the answer choices, being careful not to mix up which goes with which or to miscalculate the discriminant.
Hints
Use substitution
You are given . Try substituting this expression for in the first equation so that you have an equation in only .
Recognize the quadratic
After you substitute , expand and combine like terms. You should get a quadratic equation in ; solve it with the quadratic formula.
Find y once you know x
For each -value you find, plug it back into to get , then look for which answer choice uses one of those pairs.
Desmos Guide
Graph the circle
In Desmos, type x^2 + y^2 = 10 to graph the circle centered at the origin with radius .
Graph the line
On a new line, type y = x - 1 to graph the line from the second equation.
Locate the intersection points
Zoom in if needed and click on each point where the line intersects the circle. Desmos will display the coordinates of these intersection points; compare those coordinates to the answer choices to see which listed ordered pair matches one of them exactly.
Step-by-step Explanation
Substitute the linear equation into the circle equation
Use from the second equation in the first equation.
Substitute into :
Now expand :
Combine like terms:
Move 10 to the left to get a standard quadratic form:
Solve the quadratic equation for x
Solve using the quadratic formula. Here, , , and .
Compute the discriminant:
So,
Since , , giving
So there are two possible -values: and .
Find the corresponding y-values from y = x - 1
Now use to find for each .
- If , then
- If , then
So the system has two solution points, each pairing one of these -values with its matching -value.
Match the correct solution pair to the choices
From the work above, the two solution pairs are:
- , and
- .
Now compare these to the answer choices:
- Choice A uses the same number for and , so it does not satisfy .
- Choice B mixes the with the minus sign and the with the plus sign, so is not equal to .
- Choice C has the right pattern but uses instead of , which does not satisfy .
- Choice D matches exactly one of the two solution pairs above.
Therefore, the correct answer is D) .