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Jul 4, 2024
 #1
avatar+1250 
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Find the sum of all values of $k$ for which $x^2 + kx - 9x + 25 - 9$ is the square of a binomial.   

 

                                                                       x2 + (kx – 9x) + 16   

 

factor out x                                                      x2 + (k–9)(x) + 16

 

When posed as ax2 + bx + c, for there to be     

a double root, also called a repeated root,   

the term c must be a square and b = 2sqrt(c)  

 

Square root of 16 = +4 so b = (2)(+4) = +8                  

 

when +4 is positive                                         k – 9 = +8        

                                                                       k = +8 + 9   

                                                                       k = 17  

 

when +4 is negative                                        k – 9 = –8   

                                                                       k = –8 + 9   

                                                                       k = 1   

 

the sum of all values of k                                sum = 17 + 1   

                                                                       sum = 18   

.

Jul 4, 2024
 #1
avatar+1768 
0
Jul 4, 2024
 #1
avatar+1768 
0
Jul 4, 2024
 #1
avatar+1768 
0

Let S be the number of students who studied and NS be the number of students who did not study

 

We can represent the total number of students (T) with the following equation

 

T = S + N

 

We are given the average scores for each group and the overall class average:

 

Average score for those who studied (AS): AS = 78

 

Average score for those who did not study (ANS): ANS = 54

 

Overall class average (Avg): Avg = 70

 

We can express the total score for all students using the average scores and the number of students in each group:

 

Total score for those who studied (TS): TS = AS * S

 

Total score for those who did not study (TNS): TNS = ANS * NS

 

Total score for the entire class (Total): Total = Avg * T (since Avg represents the average score per student)

 

Since the total score for the entire class is the sum of the scores from each group:

 

Total = TS + TNS

 

We can substitute the expressions for each score:

 

Avg * T = AS * S + ANS * NS

 

Now we can substitute the values we are given:

 

70 * (S + NS) = 78 * S + 54 * NS

We can rearrange the equation to isolate NS (the number of students who did not study):

 

20 * (S + NS) = 24 * S

 

20S + 20NS = 24S

 

-4S = 20NS

 

NS = (-4/20) * S (we can divide both sides by -4 as long as S is not 0, which we can safely assume since there must be at least one student who studied)

 

NS = -(1/5) * S

 

Since NS represents a number of students, it cannot be negative. Therefore, we can flip the signs to get a positive value for the fraction representing the portion of the class that did not study:

 

NS/T = (1/5) * S/T

 

We are interested in the portion of the class that did not study, so we can express this as:

 

Fraction of class who did not study = NS/T = 1/5.

Jul 4, 2024
Jul 3, 2024

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