College Algebra : Systems of Equations

Study concepts, example questions & explanations for College Algebra

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Example Questions

Example Question #2 : Augmented Matrices

When solving a system of three linear equations in three variables using the Gauss-Jordan elimination method, your initial augmented matrix is as follows:

 

Which of the following is notation for the next step you should perform?

Possible Answers:

Correct answer:

Explanation:

When applying the Gauss-Jordan method to solve a three-by-three linear system, the objective is to use row operations to form an augmented matrix of the form

 ,

with  the solution of the system.

Once the initial augmented matrix 

 

is set up, the first step should always be to get a 1 in the upper left position; this is usually done by multiplying every element in Row 1 by the reciprocal of the first element in that row. Since the element in that position is , every element in Row 1 is multiplied by reciprocal . This step can be written using the notation .

Example Question #7 : Augmented Matrices

Use augmented matrices to solve the following system of equations:

Possible Answers:

Correct answer:

Explanation:

Begin by constructing an augmented matrix for our system of equations:

 

Switch rows 1 and 2: 

 

Add row 2 and twice row 1, to row 1: 

  

 

Divide row 1 by 5:

  

 

Subtract 3 times row 1, from row 2:

  

Divide row 2 by 2: 

  

Solution:

 

Plug the respective values of x and y into both equations to verify the solution:

Example Question #7 : Augmented Matrices

Use augmented matrices to solve the following system of equations:

Possible Answers:

Correct answer:

Explanation:

Construct an augmented matrix for our system of equations:

Swap rows 1 and 3:

   

 

Subtract 2 times row 1 from row 2: 

  

Subtract row 1 from row 3:

   

Add row 2 and three times row 3, to row 3:

  

Divide row 3 by 10:

  

Add row 3 to row 1:

  

Subtract row 3 from row 2:

  

Divide row 2 by 3:

  

Solution:

Plug the respective values of x, y, and z into all equations to verify the solution:

Example Question #1 : Non Linear Systems

Solve the following system of equations

Possible Answers:

 

There are no Real Solutions

 

 

 

 

Correct answer:

 

Explanation:

First lets solve equation 2 for y.

 

 

Now we plug in  into equation 1.

 

FOIL the left hand side, simplify and then subtract  from each side.

 

 

Now use the quadratic equation in order to solve for .

Recall the quadratic formula

 

, where  refer to the coefficients in the quadratic equation .

 

 

 

So the solutions for x are as follows

 

 

Now we just plug these values of x into equation 2 to solve for y.

 

 

 

 

 

 

So the solutions to these pair of equations are:

 

 

 

 

 

Example Question #2 : Non Linear Systems

Solve the system of equations to find the points where the graphs of the equations intersect. 

 

Possible Answers:

 ,   

 ,  

 ,   

 ,  

 ,   

Correct answer:

 ,   

Explanation:

Solve the system of equations, 

                                                                             (1)

                                                                       (2)

 

Notice that we can multiply both sides of equation (2) by  to obtain,  

                                                                           (3)

 

Now equate equations (3) and (4) to obtain, 

 

This is a quadratic equation, rearrange to find the roots by setting to zero and factoring, 

 

Use these values to find the corresponding values of  by substituting into either of the original equations. Using equation (1), 

 

 

 

 

 

 

 

The points  and  are the intersection points of the two functions, 

 

                                                                           

                                                                      

 Intersection

Example Question #3 : Non Linear Systems

Solve the following system of equations:

Possible Answers:

Correct answer:

Explanation:

 

Subtract the second equation from the first, to eliminate the y terms:

 

This yields the following: 

Factor out an x from both terms: 

Solve for x: 

Plug in the values for x into the first equation:

Therefore, when , and when 

Plug in the values for x and y to make sure they satisfy the second equation too:

Solution: 

 

Example Question #2 : Non Linear Systems

Solve the following system of equations:

Possible Answers:

Correct answer:

Explanation:

     

Substitute the value of x from the second equation, into the first equation: 

Subtract y from both sides of the equation: 

Use the quadratic formula to solve for y: 

  or   

Plug the first value of y into the first equation: 

Re-write the equation to make it easier to solve for x: 

Add  to each side of the equation:

 

The second value of y into the first equation: 

Re-write the equation to make it easier to solve for x: 

 

 Add  to each side of the equation:.

 

Plug the values of x and y into the second equation to make sure they satisfy both of them:

 

 

Solution: 

Example Question #3 : Non Linear Systems

Solve the following system of equations:

 

 

Possible Answers:

Correct answer:

Explanation:

        

Multiply the second equation by 6, to eliminate the denominator: 

Simplify: 

Plug the value of y, from the first equation, into the second equation: 

Simplify: 

Simplify further: 

Use the quadratic formula to solve for x: 

 or 

Plug the first value of x into the first equation: 

Plug the second value of x into the first equation: 

Plug the values of x and y into the second equation to make sure they satisfy both of them:

 

 

 

Solution: 

Example Question #2 : Non Linear Systems

Solve the following system of equations:

Possible Answers:

Correct answer:

Explanation:

 

Substitute the value of y from the second equation, into the first equation:

Subtract x from both sides of the equation:

Use the quadratic formula to solve for x: 

 or 

Plug the first value of x into the second equation: 

Plug the second value of x into the second equation: 

   or  

Verify the first solution by plugging the first values of x and y into both equations:

Verify the second solution by plugging the second values of x and y into both equations:

Solution: 

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