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Solve each system by substitution. $$ \begin{array}{l} -\frac{1}{4} x+\frac{3}{2} y=11 \\ -\frac{1}{8} x+\frac{1}{3} y=3 \end{array} $$

Short Answer

Expert verified
The solution is \((x, y) = (-8, 6)\).

Step by step solution

01

Solve for x in the first equation

The first equation is \(-\frac{1}{4}x + \frac{3}{2}y = 11\). Solve for \(x\) to use it in the substitution method. First, isolate \(x\):\[\frac{3}{2}y = 11 + \frac{1}{4}x\]Then, solve for \(x\):\[x = \frac{3}{2}y \times 4 - 44 = 6y - 44\]
02

Substitute x in the second equation

Substitute \(x = 6y - 44\) into the second equation: \(-\frac{1}{8}x + \frac{1}{3}y = 3\). Replace \(x\) with the expression we found in Step 1:\[ -\frac{1}{8}(6y - 44) + \frac{1}{3}y = 3\]. Simplify this equation.
03

Simplify and solve for y

Expand and simplify the equation from Step 2:\[-\frac{3}{4}y + \frac{11}{2} + \frac{1}{3}y = 3\]. Find a common denominator and simplify further. Combine the terms to solve for \(y\):\[-\frac{3}{4}y + \frac{1}{3}y = 3 - \frac{11}{2}\].\[ -\frac{9}{12}y + \frac{4}{12}y = -\frac{5}{2}\]. Simplifying gives \(-\frac{5}{12}y = -\frac{5}{2}\). Thus, \(y = 6\).
04

Substitute y back to find x

Substitute \(y = 6\) back into the expression \(x = 6y - 44\) from Step 1 to find \(x\). Compute \(x = 6(6) - 44\). Simplify to get \(x = 36 - 44 = -8\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Substitution Method
The substitution method is a popular technique for solving systems of equations, especially useful when dealing with linear equations. The idea is to solve one of the equations for one variable, and then substitute that expression into the other equation. This allows you to reduce the system to a single equation with one variable.

This method works well when one of the equations can be easily manipulated to express one variable in terms of the other. In our solution, we start by isolating \(x\) in the first equation. This step-by-step approach simplifies the process:
  • Solve one equation for one variable.
  • Substitute the expression into the other equation.
  • Simplify and solve the resulting equation.
Through these clear steps, the substitution method not only helps in tackling complex systems but also reinforces an understanding of the relationships between the variables.
Linear Equations
Linear equations form the backbone of systems of equations. These equations have one or two variables with constant coefficients; typically, they appear in the form \(ax + by = c\). Each side of a linear equation forms a straight line when graphed, hence the name.

In the given system:
  • The equation \(-\frac{1}{4}x + \frac{3}{2}y = 11\) has coefficients of \(-\frac{1}{4}\) for \(x\) and \(\frac{3}{2}\) for \(y\).
  • The second equation \(-\frac{1}{8}x + \frac{1}{3}y = 3\) involves similar structure but different coefficients.
When solved graphically, these equations will intersect at a point representing the solution.
This intersection is a core principle in understanding systems of linear equations, showcasing that solutions represent points of overlap in their respective graphs.
Algebraic Solutions
Algebraic solutions involve manipulating algebraic expressions to find the values of variables in a system of equations. Solving systems with algebraic methods like substitution involves a series of steps that require careful handling of expressions.

In our example, after expressing \(x\) in terms of \(y\), we substitute to find \(y\). This involves:
  • Simplifying by finding common denominators so both \(\frac{3}{4}y\) and \(\frac{1}{3}y\) could be combined.
  • Handling fractions with care to avoid mistakes in arithmetic.
  • Backing up the final answer by placing the solved value back into the equation - ensuring consistency of the result.
This approach not only gives the right answer but also helps develop algebraic thinking.
Understanding how variables change and interact algebraically is powerful, laying a foundation for more advanced mathematical concepts.

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Most popular questions from this chapter

For the following exercises, use this scenario: A health-conscious company decides to make a trail mix out of almonds, dried cranberries, and chocolate- covered cashews. The nutritional information for these items is shown in Table 1 . $$ \begin{array}{|c|c|c|c|} \hline & \text { Fat (g) } & \text { Protein (g) } & \text { Carbohydrates (g) } \\ \hline \text { Almonds (10) } & 6 & 2 & 3 \\ \hline \text { Cranberries (10) } & 0.02 & 0 & 8 \\ \hline \text { Cashews (10) } & 7 & 3.5 & 5.5 \\ \hline \end{array} $$ For the "hiking" mix, there are 1,000 pieces in the mix, containing \(390.8 \mathrm{~g}\) of fat, and \(165 \mathrm{~g}\) of protein. If there is the same amount of almonds as cashews, how many of each item is in the trail mix?

For the following exercises, set up the augmented matrix that describes the situation, and solve for the desired solution. At a competing cupcake store, \(\$ 4,520\) worth of cupcakes are sold daily. The chocolate cupcakes cost \(\$ 2.25\) and the red velvet cupcakes cost \(\$ 1.75 .\) If the total number of cupcakes sold per day is \(2,200,\) how many of each flavor are sold each day?

For the following exercises, create a system of linear equations to describe the behavior. Then, calculate the determinant. Will there be a unique solution? If so, find the unique solution. Three numbers add to 216 . The sum of the first two numbers is 112 . The third number is 8 less than the first two numbers combined.

For the following exercises, use the determinant function on a graphing utility. \(\left|\begin{array}{llll}1 & 0 & 8 & 9 \\ 0 & 2 & 1 & 0 \\ 1 & 0 & 3 & 0 \\\ 0 & 2 & 4 & 3\end{array}\right|\)

For the following exercises, set up the augmented matrix that describes the situation, and solve for the desired solution. A major appliance store is considering purchasing vacuums from a small manufacturer. The store would be able to purchase the vacuums for \(\$ 86\) each, with a delivery fee of \(\$ 9,200\), regardless of how many vacuums are sold. If the store needs to start seeing a profit after 230 units are sold, how much should they charge for the vacuums?

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