Why Does 40x Appear in the Quadratic Equation Transformation?

  • Thread starter Tlark10
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In summary: One should be careful because those might not be equivalent.ok elaborate please.The basic idea is that if you square both sides of an equation, the new equation might have solutions that don't satisfy the original equation. Here's a very simple example:(Eqn 1) x = -2Square both sides to get(Eqn 2) ##x^2 = 4##The first equation has -2 as its solution. The second equation has -2 and 4 as its solutions.
  • #1
Tlark10
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Homework Statement


I can't determine where the 40x comes from.
From: 4x + 5 = 8√(1 - x)
To: 16x^2 +40x + 25 = 64 - 64x^2

Homework Equations


√1-x^2 = √1-x *√x+1

The Attempt at a Solution


4x + 5 = 8√(1-x)
4x^2 + 5^2 = (8 - 8x)*(8x + 8)
16x^2 +25 = 64 - 64x^2
 
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  • #2
Tlark10 said:

Homework Statement


I can't determine where the 40x comes from.
From: 4x + 5 = 8√(1 - x)
To: 16x^2 +40x + 25 = 64 - 64x^2

Homework Equations


√1-x^2 = √1-x *√x+1

The Attempt at a Solution


4x + 5 = 8√(1-x)
4x^2 + 5^2 = (8 - 8x)*(8x + 8)
16x^2 +25 = 64 - 64x^2

What is (a+b)^2 equal to?
 
  • #3
Math_QED said:
What is (a+b)^2 equal to?
I am not sure what you mean?
 
  • #4
Math_QED said:
What is (a+b)^2 equal to?
(a+b)^2 = a^2 + b^2
 
  • #5
Tlark10 said:
(a+b)^2 = a^2 + b^2

this is a frequently made mistake.

Well (a+b)^2 = (a+b)(a+b) = ...
Use distributivity
 
  • #6
Math_QED said:
this is a frequently made mistake.

Well (a+b)^2 = (a+b)(a+b) = ...
Use distributivity
Ahhhh I see, thank you!
 
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  • #7
Tlark10 said:

Homework Statement


I can't determine where the 40x comes from.
From: 4x + 5 = 8√(1 - x)
To: 16x^2 +40x + 25 = 64 - 64x^2

Homework Equations


√1-x^2 = √1-x *√x+1

The Attempt at a Solution


4x + 5 = 8√(1-x)
4x^2 + 5^2 = (8 - 8x)*(8x + 8)
What you wrote as a relevant equation doesn't apply here. ##[8\sqrt{1 - x}]^2 \ne (8 - 8x)(8x + 8)##
Tlark10 said:
16x^2 +25 = 64 - 64x^2
 
  • #8
alternatively ##4x+5=8√(1-x)##, can be expressed as, ##(4x+5)^2=64(1-x)##
 
  • #9
chwala said:
alternatively ##4x+5=8√(1-x)##, can be expressed as, ##(4x+5)^2=64(1-x)##

One should be careful because those might not be equivalent.
 
  • #10
ok elaborate please.
 
  • #11
chwala said:
ok elaborate please.

The first equation (the original one) has one solution for x. The second one has 2 solutions for x. We use indeed that => but to make sure you can use <=> you have to say that one solution for x is not valid.
 
  • #12
chwala said:
ok elaborate please.
The basic idea is that if you square both sides of an equation, the new equation might have solutions that don't satisfy the original equation. Here's a very simple example:

(Eqn 1) x = -2
Square both sides to get
(Eqn 2) ##x^2 = 4##
The first equation has -2 as its solution. The second equation has -2 and 2 as its solutions.
 
  • #13
agreed , we can have the two solutions as stated in post 12 ,but we can go ahead and state that one solution does not satisfy the equation, my take in post number 8, is to indicate that one way of solving such quadratics is by squaring both sides, then determine later which solutions satisfy the original equation.
 

Related to Why Does 40x Appear in the Quadratic Equation Transformation?

1. How do I solve a quadratic equation?

To solve a quadratic equation, you can use the quadratic formula or factoring method. The quadratic formula is x = (-b ± √(b² - 4ac)) / 2a, where a, b, and c are the coefficients of the quadratic equation ax² + bx + c = 0. Factoring involves finding two numbers that multiply to c and add to b, which can then be used to rewrite the equation in the form (x + m)(x + n) = 0, where m and n are the two numbers.

2. What is the purpose of solving a quadratic equation?

The purpose of solving a quadratic equation is to find the values of x that make the equation true. In other words, it helps us find the solutions or roots of the equation, which can be useful in many real-world applications such as finding the maximum or minimum value of a function.

3. Can a quadratic equation have more than two solutions?

No, a quadratic equation can have at most two solutions. This is because a quadratic equation is a polynomial of degree 2, which means it can have a maximum of 2 distinct roots. However, some equations may have repeated solutions, resulting in only one distinct solution.

4. What if the quadratic equation has complex solutions?

If the quadratic equation has complex solutions, it means that the solutions involve imaginary numbers. This can happen when the discriminant b² - 4ac is negative. In this case, the solutions will be in the form of x = (-b ± √(b² - 4ac)i) / 2a, where i is the imaginary unit.

5. Can someone help me solve a quadratic equation step-by-step?

Yes, there are many resources available online that can help you solve a quadratic equation step-by-step. You can also seek help from a math tutor or teacher who can guide you through the process and explain any concepts that you may not understand.

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