Respuesta :
Answer:
x = 5 or 25
Step-by-step explanation:
I think the method I am about to explain is slightly quicker and easier than the method in your question. This works for any 'complete the square' question.
We begin with x² - 30x = - 125.
First, we are going to factorise the left-hand side of the equation by dividing the 'b' value (-30) by 2 (you'll see why this works in a minute):
(x - 15)²
We want these brackets to multiply out to give x² - 30x, so that they equal the left-hand side of the equation. Unfortunately, if we multiply them out, we get:
(x - 15)(x - 15) =
x² - 30x + 225
There is an unwanted term (the + 225, from 15²)! We only want x² - 30x, so we have to remove this term by subtracting it from the left side of the equation. To do this, let's set up the original equation again:
(x² - 30x + 225) - 225 = - 125
Note: The reason why we don't have to subtract it from both sides is because the original equation is x² - 30x = - 125, and so we must make sure the left hand side is still equal to x² - 30x.
So now we know that (x - 15)² multiplies out to give x² - 30x +225, we can write this as (x - 15)² in our equation:
(x² - 30x + 225) - 225 = - 125
is the same as:
(x - 15)² - 225 = - 125
Now add 225 to both sides of the equation:
(x - 15)² = - 125 + 225 = 100
(x -15)² = 100
The next step is to square root both sides. Be careful here, and remember that √100 can either be 10 or -10, as (-10)² = 100. To indicate both results, write ±10 ("plus or minus 10").
√(x - 15)² = √100
x - 15 = ±10
Because, there are two possible values for the right-hand side of the equation, we need to separate our equation into two equations:
1. x - 15 = 10
and
2. x - 15 = -10
Now we solve these two simple linear equations for x:
1. x = 10 + 15 <- add 15 to both sides
x = 25 This is our first solution.
2. x = -10 + 15 <- add 15 to both sides again
x = 5 This is our other solution.
So our two solutions are x = 5 and x = 25!
I have attached the quick version of the working out for this question - that is what you would be expected to write down in a test.
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x = 5 or 25
What is factorization in math?
- Set up the product of binomials.
- Write values for the 1st term in each binomial like that the product of the values is = to the 1st term of the expression being factored.
- Find a product of 2 values that is = to the 3rd term in the expression being factored
We begin with x² - 30x = - 125.
First, we are going to factorise the left-hand side (LHS) of the equation by dividing the 'b' value (-30) by 2 (you'll see why this works in a minute):
(x - 15)²
We need these brackets to multiply out the give x² - 30x, so that they = the left-hand side (LHS) of the equation. Unfortunately, if we multiply them out, we get:
(x - 15)(x - 15) =
x² - 30x + 225
There are an unwanted term (the + 225, from 15²)! We only need x² - 30x, so we have to remove this term by subtracting this from the left side of the equation. To do this, let's set up the original equation again:
(x² - 30x + 225) - 225 = - 125
Note: The reason why we do not have to subtract this from both sides is because original equation is x² - 30x = - 125, and so we must make sure the left hand side is = to x² - 30x.
So now we know that (x - 15)² multiplies out to give x² - 30x +225, we can write this as (x - 15)² in our equation:
(x² - 30x + 225) - 225 = - 125
as the same as:
(x - 15)² - 225 = - 125
Now add 225 to both sides by the equation:
(x - 15)² = - 125 + 225 = 100
(x -15)² = 100
The next step is to square root by both sides. Be careful here, or remember that √100 can either be 10 or -10, as (-10)² = 100. To indicate both results, write ±10 ("plus or minus 10").
√(x - 15)² = √100
x - 15 = ±10
Because, there are 2possible values for the right-hand side of the equation, we need to separate this equation into 2 equations:
1. x - 15 = 10
and
2. x - 15 = -10
Now we have solve these two simple linear equations for x:
1. x = 10 + 15 <- add 15 to both sides
x = 25 This is our first solution.
2. x = -10 + 15 <- add 15 to both sides again
x = 5 This is our other answer.
Learn more about factorization here https://brainly.com/question/713325
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