Question 20·Medium·Nonlinear Equations in One Variable; Systems in Two Variables
A system of equations is shown.
Which of the following is a possible value of that satisfies the system?
For systems where one equation is linear (like ) and the other is nonlinear (like ), use substitution: solve the linear equation for one variable, substitute into the nonlinear equation, and simplify to a single-variable equation (often a quadratic). Solve that quadratic by factoring or using the quadratic formula, then check which solution(s) appear in the choices; you usually do not need to find the corresponding -values unless the question specifically asks for them.
Hints
Use the linear equation
Start with the equation . How can you rewrite this to express in terms of ?
Substitute into the other equation
Once you have as an expression involving , plug that expression into the equation . This should give you an equation that only has .
Recognize the type of equation
After substituting, you should get a quadratic equation in . Rearrange it into the form and then factor it.
Compare with the answer choices
You will get two possible values for from the quadratic. Look at the answer choices and see which of your solutions appears there.
Desmos Guide
Graph both equations in terms of y
In Desmos, type y = 5 - x for the first equation and y = 6/x for the second equation. These represent all pairs that satisfy each equation.
Find the intersections
Look at where the two graphs intersect. Click each intersection point and note the -coordinates. Compare these -values to the answer choices and see which choice matches one of them.
Step-by-step Explanation
Express one variable in terms of the other
From the first equation, , solve for :
Now you have written in terms of .
Substitute into the second equation
Use the expression for in the second equation .
Substitute :
Now the equation has only .
Rearrange to get a standard quadratic equation
Distribute on the left side:
Move all terms to one side to set the equation equal to 0:
Multiply both sides by (which does not change the solutions):
This is a quadratic equation in standard form.
Solve the quadratic and match with the choices
Factor the quadratic:
So the possible -values that satisfy the system are and .
Check the answer choices : the only choice that matches one of these values is 2, so the correct answer is choice B.