To find the solution of the system of quadratic equations (points of intersection of the functions) we will act as follows:
To find the solution of the system of quadratic equations (points of intersection of the functions) we will act as follows:
Consider the following relationships between the variables x and y:
\( x^2+4=-6y \)
\( y^2+9=-4x \)
Which answer is correct?
We already learned that we should not fear the word "system". Don't worry, even when it comes to a system of quadratic equations, which are not linear, the solution is simple and straightforward.
Systems of quadratic or second-degree equations are quadratic equations written together, one next to the other or one below the other with a curly bracket, similar to what we already studied for systems of linear equations.
Generally, and would not have been given to us, therefore, they are our unknowns.
When the problem states "given the system of equations" you should know that the result has to be and that meet the conditions of said system.
The system can have one solution, two solutions, or even none.
The meaning of the solution of the system of equations is demonstrated by the points of intersection of the functions.
At those very points, the functions meet, they intersect.
These specific points exist in both the first equation and the second.
To solve a system of quadratic equations, we will use the comparison method between quadratic equations
When we have a system of quadratic equations and the isolated in this way (with the same coefficient in both equations):
We will proceed in the following order:
We will verify that the unknown is written the same way in both equations
We will compare the equations
We will find the
We will gradually place an in one of the equations to solve for its .
We will neatly record the answers found.
Note
The coefficients of the unknown and the various parameters do not necessarily have to be the same, except for the unknown . When comparing equations, first verify that the unknown is written in the same way in both equations
Let's see an example of solving a system of equations using the comparison method between quadratic equations:
Given the following system of equations:
We will proceed step by step:
We will obtain:
Let's write down this solution:
5. Let's neatly record the answers we found.
Now let's move on to the graphical method, so we can better understand the meaning of the solution to the system of equations.
Look at the rectangle in the figure.
\( x>0 \)
The area of the rectangle is:
\( x^2-13 \).
Calculate x.
Consider the following relationships between the variables x and y:
\( x^2+4=-6y \)
\( y^2+9=-4x \)
Which answer is correct?
The graphical solution of the system of quadratic equations are the points of intersection of the parabolas.
Therefore, when the parabolas are graphically represented, the solution of the system of equations will be their points of intersection.
If they do not intersect, it means that the system of equations has no solution.
If cut once, the system of equations will have one solution - the intersection point of the parabolas.
If they intersect twice, the system of equations will have two solutions - the intersection points of the parabolas.
Now, let's move on to the system of combined equations – that is, one linear and the other quadratic.
In case the system of equations is composed of a quadratic equation and a linear equation, in the following way:
Substitution method: It allows us to substitute the value of the variable y in an equation, thereby obtaining an equation with one variable.
Again, let's remember to neatly place the variable in parentheses to avoid confusion.
Note: Equations can be arranged in a different way, for example, the linear equation does not have to be represented in the same way seen previously and could have a coefficient that is not .
Let's see it in an example:
Given the system of equations (combined):
We will notice that the equations are written differently from each other (in one the is isolated and in the other it is not) and there is no problem with this.
To use the substitution method, we generally need to completely isolate one of the variables in the equations.
Now, we can place the value of (the first quadratic equation) into the linear equation and obtain a linear equation with one unknown.
Remember to use parentheses to avoid confusion.
Let's see:
Let's remove the parentheses and we will get:
Let's combine like terms and we will get:
Let's arrange the equation, transpose terms and we will get:
Let's solve with the quadratic formula and we will get:
Now, let's remember to place the found values to find the values and thus be able to reach a complete result.
We will start with and place it in one of the original equations (the one that seems simpler - which is generally the linear one)
We will get:
Let's write this solution:
Now let's place the second we found, in one of the original equations and we will get:
Let's write this solution:
Let's neatly note down the solutions found
These are the points of intersection of the line with the parabola.
Look at the rectangle in the figure.
\( x>0 \)
The area of the rectangle is:
\( x^2-13 \).
Calculate x.
Consider the following relationships between the variables x and y:
\( x^2+4=-6y \)
\( y^2+9=-4x \)
Which answer is correct?
Parabolas located on the same Cartesian plane can intersect more than once.
To find the intersection points between the parabolas, we should compare their equations, as we have learned, when appears in the same way in both equations (with the same coefficient).
By comparing the equations, we will arrive at an equation with one unknown .
We will solve for the value of and alternately place in each of the equations the value of to discover .
If we arrive at one solution, it means that the parabolas intersect only once.
If we arrive at two solutions, it means that the parabolas intersect twice.
If we find that there is no solution, it means that the parabolas do not intersect at all.
Useful Information
In some cases, as in the example, the parabolas may intersect when
And the question will be what are the intersection points of the parabolas.
To find the intersection points, we simply place in one of the given parabola equations and thus discover the point.
We must convert verbal math problems into quadratic equations to solve them
Just as we have already done, equations are constructed based on the text given in the problem.
How will we do it?
The key to solving problems of this type is to describe the unknowns through a single unknown .
This way instead of arriving at two equations with two unknowns we will arrive at one quadratic equation.
Another very important issue is to read and understand exactly what the problem is telling us. This way we can construct the equation correctly.
Let's see an example:
Find two numbers whose sum equals and the sum of these squared equals
Solution:
First, let's define the variables with one unknown
First number:
Second number:
How have we defined the second number?
We know that the sum of the two numbers we are looking for is
Think about this: let's say the second number was ,
we would write
and isolate the
We would get
Magnificent. Now let's move on to the second part of the problem: the sum of the numbers squared equals That is, if we square each of the numbers and then add them we will get
Let's translate it into an equation:
Great! Now let's remove the parentheses using the distributive property of multiplication and we will arrive at a sorted quadratic equation:
Let's combine terms and we will get:
Great! We can solve this quadratic equation easily with the quadratic formula. Let's solve and we will get to:
Pay attention! These are not the two numbers we are looking for! These are possible solutions for the first number.
Now we must find what the second number would be in each of these possibilities.
Let's begin:
When the first number is ,
the second is and therefore, .
When the first number is ,
the second is and therefore .
Look at the rectangle in the figure.
\( x>0 \)
The area of the rectangle is:
\( x^2-13 \).
Calculate x.
Consider the following relationships between the variables x and y:
\( x^2+4=-6y \)
\( y^2+9=-4x \)
Which answer is correct?
The quadratic inequality describes in which interval the function is positive and in which it is negative.
You have already studied all the steps to solve an inequality of this type.
Before we begin to learn how to solve the quadratic inequality, it is advisable to remember two important things:
Excellent, now we can begin.
When we have a quadratic inequality, we will act following these steps:
Solve the following inequality:
Solution:
Let's proceed step by step:
Let's find the points of intersection with the axis
According to the quadratic formula, we will obtain:
We will identify, according to the coefficient of , that the parabola opens upwards.
Let's calculate the corresponding interval according to the exercise and the scheme.
Since the exercise asks when the quadratic equation is less than , they are asking about the interval of negativity, therefore, by observing the scheme we can determine that the quadratic equation is less than when :
This is the solution to the inequality.
Consider the following relationships between the variables x and y:
Which answer is correct?
Look at the rectangle in the figure.
x>0
The area of the rectangle is:
.
Calculate x.
Look at the rectangle in the figure.
\( x>0 \)
The area of the rectangle is:
\( x^2-13 \).
Calculate x.
Consider the following relationships between the variables x and y:
\( x^2+4=-6y \)
\( y^2+9=-4x \)
Which answer is correct?