College Algebra : Solving Equations and Inequallities

Study concepts, example questions & explanations for College Algebra

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Example Questions

Example Question #2 : Quadratic Equations

Solve 

Possible Answers:

Correct answer:

Explanation:

First, we must factor out any common factors between the two terms.  Both 3 and 12 share a factor of 3, so we can "take" 3 out, like this:

.

Inside the parentheses, it becomes clear that this is a difference of squares problem (a special factor), which can be solved with the equation

.

Thus, 

Now, we can set each factor to 0, and solve for :

and

.

Example Question #201 : Equations / Inequalities

Solve for x.

Possible Answers:

x = –2/3, –3

x = –5, 5

x = –2/5, –5

x = –5/2, –5

x = –5

Correct answer:

x = –5/2, –5

Explanation:

1) The first step would be to simplify, but since 2, 15, and 25 have no common factors greater than 1, simplification is impossible.

Now we factor. Multiply the first coefficient by the final term and list off the factors.

2 * 25 = 50

Factors of 50 include:

1 + 50 = 51

2 + 25 = 27

5 + 10 = 15

2) Split up the middle term to make factoring by grouping possible.

Note that the "2" and the "10," and the "5" and the "25," have to go together for factoring to come out with integers. Always make sure the groups actually have a common factor to pull.

3) Pull out the common factors from both groups, "2x" from the first and "5" from the second.

4) Factor out the "(x+5)" from both terms.

5) Set each parenthetical expression equal to zero and solve.

2x + 5 = 0,  x = –5/2

x + 5 = 0, x = –5

Example Question #1 : Quadratic Equations

Use the quadratic formula to find the solutions to the equation.

Possible Answers:

and 

 and 

 and 

 and 

 and 

Correct answer:

and 

Explanation:

The quadratic formula is as follows:

We will start by finding the values of the coefficients of the given equation:

Quadratic equations may be written in the following format:

In our case, the values of the coefficients are:

Substitute the coefficient values into the quadratic equation:

After simplifying we are left with:

leaving us with our two solutions:

 and 

Example Question #5 : Quadratic Equations

Solve for x:

Possible Answers:

Correct answer:

Explanation:

To solve for x, we must first simplify the trinomial into two binomials.

To simplify the trinomial, its general form given by , we must find factors of  that when added give us . For our trinomial,  and the two factors that add together to get  are  and .

Now, using the two factors, we can rewrite  as the sum of the two factors each multiplied by x:

Next, we group the first two and last two terms together and factor each of the groups:

Now, simplify further:

Finally, set each of these binomials equal to zero and solve for x:

Example Question #41 : Solving Equations And Inequallities

Solve for  with the given quadratic equation:

Possible Answers:

Correct answer:

Explanation:

To solve for , we can use the quadratic formula:

 

Example Question #11 : Quadratic Equations

Solve the following quadratic equation by completing the square:

 

Possible Answers:

   

Correct answer:

   

Explanation:

Add 3 to both sides of the equation, to isolate the x terms: 

Divide each term by 8, to isolate the x2 term: 

Add the square of one half of the "b" term to each side:

Simplify: 

Simplify further: 

Use the following factoring rule to simplify the left side of the equation: 

Take the square root of both sides of the equation: 

Simplify: 

Subtract one eighth from each side of the equation:  or 

Simplify the equations: 

Solution: 

Example Question #461 : College Algebra

A farmer is building a fence around a field. He knows that the length of the field is 11 meters more than twice its width. If he knows that the area of the field is 30 square meters, what is the perimeter, in meters, of the field?

Possible Answers:

45

19

17

34

30

Correct answer:

34

Explanation:

In order to find the perimeter, start by defining the variables. It is typically easier to define one of the variables in terms of the other; therefore, only one unknown will need to be calculated to find the perimeter. The problem states that the length is eleven more than twice the width; thus, we can define our variables in the following way:

The farmer knows that the field's area is thirty square meters. Area is found using the following formula:

Substitute in the known value for the area and the defined variables for the length and width. 

Notice that this equation possesses all the components of a quadratic. Use the information in the equation to construct a quadratic equation that can be factored to obtain an answer. Start by multiplying the first term by the variable on the right side of the equation.

In order to make the quadratic equal to zero, subtract 30 from both sides of the equation. 

Now, factor the quadratic and solve for the variable. We can use the ac method to solve for the variable. Quadratics can be written in the following format:

We need to find two numbers whose product equals a multiplied by c and whose sum equals b; therefore, the product of the factors must be -60 and their sum must equal 11. Write out the prime factorization of 60.

There is one factor of -60 that when added together sum to equal 11: 15 and -4.

Use the factors and split the middle term in the quadratic in order to make factoring by grouping possible.

Pull the greatest common factor from each pair of terms:  from the first and 15 from the second.

Factor out the quantity  from both terms.

Set each factor equal to zero and solve for w.

We can cross out the this negative option because the width of a dimension cannot be a negative value. Solve for w in the second factor.

The width of the field is 2 meters. Substitute 2 in for the variable and solve for the perimeter.

Perimeter is found using the formula:

The perimeter of the field is 34 meters.  

Example Question #1 : Applications Of Quadratic Equations

Quadratic equations appear often in physics. The basic kinematic equations for the position  of a particle as a function of time , with an initial velocity  (a constant) and constant acceleration  can be written as, 

 

 

This is a quadratic function in . The function therefore gives the position as a quadratic function of time . If we are dealing with a free-falling object under Earth's gravitational field, we might write this function in the form, 

to express the "height"  of the object at a given time  falling with a constant acceleration . Here  the initial height (a constant). The units for acceleration are meters-per-square second . The negative acceleration is a convention to signify that the direction of the acceleration is downward. 

 

 

Find the time required for a ball dropped from a height of 100 m from rest to reach the ground using the quadratic function for height written below,  

 

(Hint, what is the value of the height  when the ball strikes the ground?).

Possible Answers:

 

Correct answer:

 

Explanation:

We're given the function,  

We know that the gravitational acceleration on earth is: 

 (meters-per-square second)

 

Because the ball starts at rest, the initial velocity  is zero, 

 (meters-per-second) 

 

We are given the initial height, 

 (meters) 

 

When the ball reaches the ground, the height is "zero," so the value of  is zero at this time, and so we have: 

 

  (units omitted in the equation).

 

 

 

(Note that although taking the square root of both sides of an equation will produce positive and negative solutions, we ignore the negative solution since "negative time" makes no sense in the context of this problem).

 

 

Example Question #1 : Applications Of Quadratic Equations

A sidewalk on a street corner reaches from a library to a bookstore making an L shape around that corner. The L shaped path has one length that is twice as long as the other. The diagonal path being built between the two buildings will be 102 feet long. How many feet shorter is the diagonal path than the traditional L shaped path around the corner?

Possible Answers:

The diagonal path would be longer.

Correct answer:

Explanation:

Use Pythagorean Theorem to solve.

Since the path around the corner is 3x, 3 times the   is approximately 137. The distance saved is 137-102= 35 feet.  Note that we only needed the positive square root since we cannot have a negative distance.

Example Question #1 : Equations Reducible To Quadratic Form

Solve 

Possible Answers:

There are no solutions

Correct answer:

Explanation:

To make this problem easier, lets start off by doing a u-substitution.

Let .

Now we can factor the left hand side.

We have two solutions for , now we can plug those into , to get all the solutions.

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