introduction
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Introduction - PowerPoint PPT PresentationTRANSCRIPT
IntroductionPreviously, we learned how to solve quadratic-linear systems by graphing and identifying points of intersection. In this lesson, we will focus on solving a quadratic-linear system algebraically. When doing so, substitution is often the best choice. Substitution is the replacement of a term of an equation by another that is known to have the same value.
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5.4.2: Solving Systems Algebraically
Key Concepts• When solving a quadratic-linear system, if both
functions are written in function form such as “y =” or “f(x) =”, set the equations equal to each other.
• When you set the equations equal to each other, you are replacing y in each equation with an equivalent expression, thus using the substitution method.
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5.4.2: Solving Systems Algebraically
Key Concepts
• You can solve by factoring the equation or by using
the quadratic formula, a formula that states the
solutions of a quadratic equation of the form
ax2 + bx + c = 0 are given by
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5.4.2: Solving Systems Algebraically
Common Errors/Misconceptions• miscalculating signs • incorrectly distributing coefficients
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5.4.2: Solving Systems Algebraically
Guided PracticeExample 1Solve the given system of equations algebraically.
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5.4.2: Solving Systems Algebraically
Guided Practice: Example 1, continued1. Since both equations are equal to y,
substitute by setting the equations equal to each other.
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5.4.2: Solving Systems Algebraically
–3x + 12 = x2 – 11x + 28 Substitute –3x + 12 for y in the first equation.
Guided Practice: Example 1, continued2. Solve the equation either by factoring or
by using the quadratic formula. Since a (the coefficient of the squared term) is 1, it’s simplest to solve by factoring.
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5.4.2: Solving Systems Algebraically
–3x + 12 = x2 – 11x + 28 Equation
0 = x2 – 8x + 16
Set the equation equal to 0 by adding 3x to both sides, and subtracting 12 from both sides.
0 = (x – 4)2 Factor.
Guided Practice: Example 1, continued
Substitute the value of x into the second equation of the system to find the corresponding y-value.
For x = 4, y = 0. Therefore, (4, 0) is the solution.
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5.4.2: Solving Systems Algebraically
x – 4 = 0 Set each factor equal to 0 and solve.
x = 4
y = –3(4) + 12 Substitute 4 for x.y = 0
Guided Practice: Example 1, continued3. Check your solution(s) by graphing.
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5.4.2: Solving Systems Algebraically
Guided Practice: Example 1, continuedThe equations do indeed intersect at (4, 0); therefore, (4, 0) checks out as the solution to this system.
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5.4.2: Solving Systems Algebraically
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Guided Practice: Example 1, continued
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5.4.2: Solving Systems Algebraically
Guided PracticeExample 2Solve the given system of equations algebraically.
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5.4.2: Solving Systems Algebraically
Guided Practice: Example 2, continued1. Since both equations are equal to y,
substitute by setting the equations equal to each other.
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5.4.2: Solving Systems Algebraically
x – 1 = 2x2 + 13x + 15 Substitute x – 1 for y in the first equation.
Guided Practice: Example 2, continued2. Solve the equation either by factoring or
by using the quadratic formula. Since the equation can be factored easily, choose this method.
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5.4.2: Solving Systems Algebraically
x – 1 = 2x2 + 13x + 15 Equation
0 = 2x2 + 12x + 16
Set the equation equal to 0 by subtracting x from both sides and then adding 1 to both sides.
0 = 2(x + 2)(x + 4) Factor.
Guided Practice: Example 2, continuedNext, set the factors equal to 0 and solve.
Substitute each of the values you found for x into the second equation of the system to find the corresponding y-value.
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5.4.2: Solving Systems Algebraically
x + 2 = 0 x + 4 = 0
x = –2 x = –4
y = (–2) – 1 Substitute –2 for x.
y = –3
Guided Practice: Example 2, continued
For x = –2, y = –3, and for x = –4, y = –5. Therefore, (–2, –3) and (–4, –5) are the solutions to the system.
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5.4.2: Solving Systems Algebraically
y = (–4) – 1 Substitute –4 for x.
y = –5
Guided Practice: Example 2, continued3. Check your solution(s) by graphing.
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5.4.2: Solving Systems Algebraically
Guided Practice: Example 2, continuedThe equations do indeed intersect at (–2, –3) and (–4, –5); therefore, (–2, –3) and (–4, –5) check out as the solutions to this system.
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5.4.2: Solving Systems Algebraically
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Guided Practice: Example 2, continued
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5.4.2: Solving Systems Algebraically