1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
AleksandrR [38]
2 years ago
8

Help with question 5a

Mathematics
1 answer:
Llana [10]2 years ago
5 0
This is a refreshing question!

We are given that
f(r)=ar+b, and
Sum f(r) =125 for r=1 to 5
Sum f(r) = 475 for r=1 to 10.

and we know, using Gauss's method, that
G(n)=sum (1,2,3.....n) = n(n+1)/2 or
G(n)=n(n+1)/2

Sum f(r) =125 for r=1 to 5
=>
sum=a(sum of 1 to 5) + 5b => G(5)a+5b=125   [G(5)=15]
15a+5b=125 ...................................................(1)

Similarly, Sum f(r) =  475 for r=1 to 10 => G(10)a+5b=475  [G(10)=55]
=>
55a+10b=475.................................................(2)

Solve system of equations (1) and (2)
(2)-2(1)
55-2(15)a=475-2(125) => 25a=225 =>
a=9

Substitute a=9 in 1 => 15(9)+5b=125 => 5b=-10
b=-2

Substitute a and b into f(r), 
f(r)=9r-2
check: sum f(r), r=1,5 = (9-2)+(18-2)+(27-2)+(36-2)+(45-2)=135-10=125 [good]

We define the sum of f(r) for r=1 to n as
S(n)=sum f(r) for r=1 to n = 9(sum 1,2,3....n)-2n = 9n(n+1)/2-2n = 9G(n)-2n
S(n)=9n(n+1)/2-2n
checks:
S(5)=9(15)-2(5)=135-10=125  [good]
S(10)=9(55)-2(10)=495-20=475 [good]

Hence 
(a)
S(n)=sum f(r) for r=1,n
= 9(sum i=1,n)+n(-2)
= 9(n(n+1)/2 -2n
=(9(n^2+n)/2) -2n

(b) sum f(r) for i=8,18
=sum f(r) for i=1,18  -  sum f(r) for i=1,7
=S(18)-S(7)
=(9(18^2-18)/2-2(18))-(9(7^2-7)/2-2(7))
=1503-238
=1265
You might be interested in
A car travels a distance of 230 miles in a time of 4.2 hours. What is its average speed rounded to 1dp?
zhannawk [14.2K]

Its  average speed rounded to 1dp is 54.76 miles per hour.

<h3>Average speed</h3>

Using this formula

Average speed=Distance/Time

Where:

Total Distance =230 miles

Time= 4.2 hours

Let plug in the formula

Average speed=230/4.2

Average speed=54.76

Inconclusion Its  average speed rounded to 1dp is 54.76 miles per hour.

Learn more about average speed here:brainly.com/question/4931057

5 0
2 years ago
Read 2 more answers
Use &lt; , &gt; , = , ≤ , ≥ to complete these statements. 1) if x &lt; y , then y___ x, 2) if x &gt; 5 and 5 &gt; y, then x ___
vodomira [7]

Answer:

1) y > x

2) x > 5 > y

3) x ≤ 4  ( or 4 ≥ x )

4) x = y

Step-by-step explanation:

1) 1. y is greater than x

  2. so y > x

2) 1. 5 is less than x and more than y

   2. we can write this like x > 5 > y

   3. you can just squish them together as a shortcut usually: x > 5 and 5 > y      -->      x > 5 > y

3) 1. x is for at most, we can say this as x is less than or equal to 4

   2. this is written as x ≤ 4  or  4 ≥ x

4) 1. x - y = 0 so x and y must be the same value

   2. therefore x = y

4 0
2 years ago
Raj’s bathtub is clogged and is draining at a rate of 1. 5 gallons of water per minute. The table shows that the amount of water
Morgarella [4.7K]

Answer:

Draining rate is at 1.5 gallons per minute

That would be y = 1.5g / x.

From the function or the equation, here is the answer.

The range would be all real numbers such that 0 ≤ y ≤ 40.

Step-by-step explanation:

7 0
2 years ago
Identify the polygon that is the shape of the United States flag.
Rudiy27

Answer:

rectangle

Step-by-step explanation:

Polygons are named according to the number of sides and angles they have. The most familiar polygons are the triangle, the rectangle, and the square. A regular polygon is one that has equal sides. Polygons also have diagonals, which are segments that join two vertices and are not sides.

3 0
3 years ago
No link need right answer
SCORPION-xisa [38]

Answer:

Step-by-step explanation:

The ans is 13 to 7

4 0
3 years ago
Read 2 more answers
Other questions:
  • Graph y= 2x-2 with the domain (1,2,3)
    11·1 answer
  • A falling object accerlates from -10.0m/s to -30.0m/s how much time does that take
    14·1 answer
  • <img src="https://tex.z-dn.net/?f=x%5E%7B2%7D%20-%2022x%20%2B121" id="TexFormula1" title="x^{2} - 22x +121" alt="x^{2} - 22x +12
    9·1 answer
  • Y = x2 + 13<br> Non linear or linear
    13·1 answer
  • Someone add me on snap im bored
    7·2 answers
  • Can you help me please
    7·1 answer
  • Point X is at 2/3 on a number line. On the same number line, point Y is the sane distance for 0 as point X, but has a numerator
    15·1 answer
  • Which figure has the largest shaded region?
    12·2 answers
  • What is the angle of rotation counterclockwise about the spinner’s center that maps label h to label A? 252° 324° 144° 216°
    13·2 answers
  • The original price of a mirror was priced at $15 but was on sale. The amount of the discount is $3. What percent is the discount
    15·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!