Question 89·Medium·Linear Equations in One Variable
In the equation , what is the value of ?
For equations where the same grouped expression (like ) appears multiple times, first get all those terms on one side and factor them, or directly combine them using properties of equality. Then simplify to a basic linear equation in , solve carefully, and finally substitute back into the specific expression the question asks for—double-checking that you report the value of that expression, not just the value of .
Hints
Look for repeated groups
Notice that the expression appears in more than one place in the equation. Think about how you could combine those terms.
Move all (3y − 2) terms to one side
Try subtracting from both sides so that all the terms are on the same side of the equation.
Clear common factors, then solve
Once you have something like , divide both sides by 5, solve the resulting linear equation for , and then plug that value into —the expression the question asks for.
Desmos Guide
Graph the two sides of the equation
In Desmos, enter the left-hand side as one function and the right-hand side as another:
- Type
f(y) = 7(3y - 2) - Type
g(y) = 5(y + 6) + 2(3y - 2)Then look for the intersection point of the graphs of and ; its -coordinate is the value of that satisfies the equation.
Compute 3y − 2 using the solution for y
Once you know the value of from the intersection, add a new line in Desmos and type 3*(value_of_y) - 2 (replacing value_of_y with the number you found). The output of this expression is the value of that you need for the answer choice.
Step-by-step Explanation
Combine like grouped terms
Start with the equation:
Notice that appears on both sides. Subtract from both sides to combine those terms on the left:
Now factor on the left:
So you get:
Simplify the equation by dividing
Both sides of the equation are multiplied by 5, so divide both sides by 5:
Now you have a simple linear equation relating and .
Solve for y
Solve :
- Subtract from both sides:
which simplifies to
- Add 2 to both sides:
- Divide both sides by 2:
Find the value of 3y − 2
Now substitute into :
So the value of is 10.