Question 32·Medium·Linear Equations in One Variable
In the equation , and are constants. If the equation is true for all real values of , what are the values of and ?
For equations that must hold for all real , first distribute and simplify each side into the form . Then equate the coefficients of and the constant terms separately to get a small system of equations in the unknown constants. Solve this system step by step (usually starting with the equation that has only one unknown), and finally verify that your pair matches one of the answer choices and makes both sides of the original equation identical.
Hints
Start by expanding
Distribute on the left and on the right so that you remove the parentheses and see the coefficients of clearly.
Write in the form (coefficient)x + constant
After expanding, rewrite each side so it looks like . Identify the coefficient of and the constant term on each side.
Use "true for all x"
If two linear expressions are equal for every real , their -coefficients must be equal, and their constant terms must be equal. Turn this idea into two separate equations in and .
Solve the system step by step
Use the simpler equation (the one with only ) to find first, then plug that value into the other equation to find .
Desmos Guide
Rewrite as coefficient and constant equations
From the algebra, you have two equations: (from matching x-coefficients) and (from matching constants).
Find p using graphing
In Desmos, graph y = 4x and y = 6. The x-coordinate of their intersection gives the value of .
Use that p to find q
Once you have , graph y = x + p_value and y = 15 (replacing p_value with your result). The x-coordinate of the intersection is the value of .
Confirm with the original equation
Plug your and values into y1 = p*(4x+1)+q and y2 = 3*(2x+5). The two lines should overlap completely if you found the correct values.
Step-by-step Explanation
Distribute on both sides
Start by expanding each side of the equation:
Left side:
Right side:
So the equation becomes:
Match the structure of both sides
Think of both sides as "coefficient of " plus "constant term":
- Left side: coefficient of is , constant term is .
- Right side: coefficient of is , constant term is .
Because the equation is true for all real , these matching parts must be equal:
- Coefficient of :
- Constant term:
Solve for p from the coefficient equation
Solve the first equation :
Now you know the value of , and you will use it in the constant-term equation to find .
Solve for q and match the answer choice
Substitute into :
Subtract from both sides:
So and , which corresponds to choice D.