Look at the pentagonal numbers. Use finite differences to determine which function represents the pattern.
2 answers:
Answer:
f(x) = 1.5x - 0.5x
Step-by-step explanation:
The function of the pattern represented by the pentagonal numbers is the sum of three triangular numbers.
The triangular number general formula
x (x + 1) / 2
For example,
The sequence
1, 3, 6, 10
*
* * *
* * * * * *
* , * *, * * *, * * * *
_____________________________
The pentagonal numbers
The sequence:
1, 5, 12, 22, 35
As shown in the picture can be divided into three triangles
Triangle 2
x (x + 1) / 2
Triangle 1 and 3 (they are triangles one unit smaller than 2)
n (n + 1) / 2
n= x-1
Replacing n
(x-1) ((x-1) + 1) / 2
(x-1) (x) / 2
(x-1) x / 2
______________
Function represents the pattern
Triangle 2 + (Triangle 1 + Triangle 3)
Triangle 1 = Triangle 3
So then,
Triangle 2 + 2* Triangle 1
x (x +1) /2 + 2* (x -1) x/2
Rearranging
0.5 x (x +1) + x(x -1)
0.5x^2 + 0.5x + x^2 -x
(0.5 x^2 + x^2) + (0.5x -x )
1.5 x^2 - 0.5 x
______
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Answer:
<u>The number is 296.</u>
Step-by-step explanation:
Let's call "x" to the number we are looking for.
Now, the problem states that "5 more than the quotient of a number and 8 is 42". This means that this number is being divided by 8, it's also being additioned 5 and the final result is 42. Therefore, the expression of this operations on this number is the following:
. Let's solve the equation to find x.
1. Write the expression.
2. Substract 5 from both sides and simplify.
3. Multiply 8 on both sides and simplify.
<u>We have found our number, it's 296!</u>
keep in mind that, a negative coefficient to "x", will make the graph reflect over the y-axis.