Question 218·Medium·Nonlinear Equations in One Variable; Systems in Two Variables
The equation
is given.
What is the positive solution to the equation?
(Express the answer as an integer)
For quadratic equations with integer coefficients, quickly check if they factor into simple binomials by looking for two numbers whose product is and sum is . If factoring works, apply the zero product property to get both roots, then pay close attention to what the question actually requests (for example, only the positive root, the larger root, or the sum of the roots) so you report the correct value without doing extra work.
Hints
Identify the equation type
Notice that the equation has an term, an term, and a constant. What kind of equation is this, and what methods can you use to solve it?
Try factoring
See if you can factor into a product of two binomials of the form .
Use the product and sum of numbers
You need two numbers that multiply to and add to . Think about factor pairs of that sum to .
Finish after factoring
Once you have factored the quadratic, set each factor equal to zero to find both solutions, then decide which one matches what the question is asking for.
Desmos Guide
Enter the quadratic equation
In Desmos, type y = 5x^2 - 11x - 12 to graph the quadratic function.
Find the x-intercepts
Look for the points where the graph crosses the x-axis. Click on each x-intercept; Desmos will display their coordinates. The x-coordinates of these intercepts are the solutions to the equation.
Choose the requested solution
Among the x-intercepts you see, identify which x-value is positive. That is the positive solution to the equation.
Step-by-step Explanation
Recognize the type of equation
The equation is a quadratic equation in standard form , where , , and . Quadratic equations can often be solved efficiently by factoring.
Factor the quadratic expression
We want to factor into the form .
Look for two numbers that multiply to and add to . Those numbers are and .
Rewrite the middle term using and :
Now factor by grouping:
Factor out :
Set factors to zero and prepare to solve
We now have
For a product to be zero, at least one factor must be zero:
Solve each linear equation to obtain two real roots—one negative and one positive. We will identify the requested solution in the next step.
Select the positive solution
The two solutions are and . The question specifically asks for the positive solution, so we choose .
Final answer: .