Question 62·Medium·Linear Equations in One Variable
If is the solution to the equation above, what is the value of ?
For linear equations with parentheses, first use the distributive property carefully to remove parentheses, then combine like terms to simplify. Isolate the variable step by step, watching signs and arithmetic. If the question asks for an expression like , look for a way to manipulate your simpler equation (such as ) directly to that expression, which can avoid working with fractions and save time; finally, match your result to the choices, checking any last-step arithmetic.
Hints
Remove the parentheses
Look at the terms and . How can you use the distributive property to rewrite each without parentheses?
Simplify the equation
After distributing, combine like terms on the left side (group the -terms together and the constant numbers together), then start moving variable terms to one side and constants to the other.
Aim directly for
Once you get a simple equation like , think about how to turn it into an equation involving and then , instead of first solving for as a fraction.
Desmos Guide
Graph both sides of the equation
In Desmos, use as the variable. In one line, enter f(x) = 5(4x + 2) - 3(2x - 4). In another line, enter g(x) = 8x + 26. These represent the left and right sides of the equation.
Find the solution for the variable
Look for the intersection point of the graphs of and . The -coordinate of this intersection is the value that makes the original equation true (this is the same as the -value in the problem statement). Note this -value.
Use Desmos to evaluate
In a new line, type 9*(value) + 1, replacing value with the -coordinate you found at the intersection (for example, if the intersection is at , type 9*a + 1). The number Desmos outputs is the value of ; compare this with the answer choices.
Step-by-step Explanation
Distribute to remove parentheses
Use the distributive property on both grouped terms.
- Multiply by each term in .
- Multiply by each term in .
This gives
So the equation becomes
Combine like terms on the left side
Combine the -terms and the constants on the left:
So the equation simplifies to
Isolate the -term
Move all -terms to one side and constants to the other.
Subtract from both sides:
Now subtract from both sides:
Divide both sides by to get a simpler equation:
Find directly from
You want , and you already know that .
Multiply both sides of by to get an equation for :
Now add to both sides to match the expression :
So , which corresponds to answer choice C) 7.