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3 years ago

Show how to make a ten to solve 13-7

Mathematics

2 answers:

lara [203]3 years ago

6 0

13-7=?

13-7 = 6

************* - ******* = ******

emmainna [20.7K]3 years ago

3 0

You can do 13-7 then counter seven away from 13 and you'll get your answer

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C=1/21.22.23+1/22.23.24+................+1/200.201.202 . = là dấu nhân

Aneli [31]

It looks like you have to find the value of the sum,

$C = \displaystyle \frac1{21\times22\times23} + \frac1{22\times23\times24} + \cdots + \frac1{200\times201\times202}$

so that the n-th term in the sum is

$\dfrac1{(21+(n-1))\times(21+n)\times(21+(n+1))} = \dfrac1{(n+20)(n+21)(n+22)}$

for 1 ≤ n ≤ 180.

We can then write the sum as

$\displaystyle C = \sum_{n=1}^{180} \frac1{(n+20)(n+21)(n+22)}$

Break up the summand into partial fractions:

$\dfrac1{(n+20)(n+21)(n+22)} = \dfrac a{n+20} + \dfrac b{n+21} + \dfrac c{n+22}$

Combine the fractions into one with a common denominator and set the numerators equal to one another:

$1 = a(n+21)(n+22) + b(n+20)(n+22) + c(n+20)(n+21)$

Expand the right side and collect terms with the same power of n :

$1 = a(n^2+43n+462)+b(n^2+42n+440) + c(n^2+41n + 420) \\\\ 1 = (a+b+c)n^2 + (43a+42b+41c)n + 462a+440b+420c$

Then

a + b + c = 0

43a + 42b + 41c = 0

462a + 440b + 420c = 1

==> a = 1/2, b = -1, c = 1/2

Now our sum is

$\displaystyle C = \sum_{n=1}^{180} \left(\frac1{2(n+20)}-\frac1{n+21}+\frac1{2(n+22)}\right)$

which is a telescoping sum. If we write out the first and last few terms, we have

C = 1/(2×21) - 1/22 + 1/(2×23)

… … + 1/(2×22) - 1/23 + 1/(2×24)

… … + 1/(2×23) - 1/24 + 1/(2×25)

… … + 1/(2×24) - 1/25 + 1/(2×26)

… … + … - … + …

… … + 1/(2×198) - 1/199 + 1/(2×200)

… … + 1/(2×199) - 1/200 + 1/(2×201)

… … + 1/(2×200) - 1/201 + 1/(2×202)

Notice the diagonal pattern of underlined and bolded terms that add up to zero (e.g. 1/(2×23) - 1/23 + 1/(2×23) = 1/23 - 1/23 = 0). So, like a telescope, the sum collapses down to a simple sum of just six terms,

C = 1/(2×21) - 1/22 + 1/(2×22) + 1/(2×201) - 1/201 + 1/(2×202)

which we simplify further to

C = 1/42 - 1/44 - 1/402 + 1/404

C = 1,115/1,042,118 ≈ 0.00106994

4 0

3 years ago

What types of symmetry dose the uppercase N have

mel-nik [20]

N doesn’t have any lines of symmetry!

5 0

3 years ago

Y=-2|x+2|-4 i need to find y intercept and the x intercept

NeTakaya

Answer:

x-int: ∅

y-int: (0,-8)

Step-by-step explanation:

To find the x and y-intercept, simply plug in zero for x and y:

$0=-2|x+2|-4\\4=-2|x+2|\\-2=|x+2|\\$

Because an absolute value cannot be equal to a negative, there is no x-intercept.

$y=-2|0+2|-4\\y=-2|2|-4\\y=-4-4\\y=-8$

Hope it helps :)

3 0

2 years ago

Which of the sets of ordered pairs represents a function?

iogann1982 [59]

(x,y)
if x repeats with a differnt y then it is not a function

A. none of them repeat, it's a function
B. none of them repeat, it's a function

both of them are functions

5 0

3 years ago

What is the eighth term in the arithmetic sequence defined by the explicit formula an=2n+7?

svetoff [14.1K]

2n+7
2 x 8+8
16+8
24
24 is the answer

8 0

3 years ago

Read 2 more answers