C1 Question simple Watch

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Mushu
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#1
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evalute: sigma (7+2r) with 30 on top of the sigma and r=10 at the bottom.

I used Sn= n/2 {a + L) and everything is correct except the value of n I have. I put n = 30-10 = 20 terms. But the markscheme says n=30-9= 21 terms Why?
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r2they
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#2
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N= all the numbers from 10 to 30

That is:

1. 10
2. 11
3. 12
4. 13
5. 14
6. 15
7. 16
8. 17
9. 18
10. 19
11. 20
12. 21
13. 22
14. 23
15. 24
16. 25
17. 26
18. 27
19. 28
20. 29
21. 30

21 values of N
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El Stevo
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the terms are inclusive of both 30 and 10, so there always one more than the difference of the two numbers. if you dont belive me, count them...

10,11,12,13,14,15,16,17,18,19
20, 21, 22, 23, 24, 25, 26, 27, 28, 29
30 == 21 numbers
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Aitch
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(Original post by littlemisshala)
evalute: sigma (7+2r) with 30 on top of the sigma and r=10 at the bottom.

I used Sn= n/2 {a + L) and everything is correct except the value of n I have. I put n = 30-10 = 20 terms. But the markscheme says n=30-9= 21 terms Why?

To save typing a long list:

The sum of terms 10 to 30 is the sum of terms 1 to 30, but omitting the first 9. i.e. 21 terms.

Aitch
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Mushu
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Thanks...can anyone do:

The curve C has the equation
y = x2 + ax + b,
where a and b are constants.
Given that the minimum point of C has coordinates (−2, 5), find the values of a and b.
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Aitch
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(Original post by littlemisshala)
Thanks...can anyone do:

The curve C has the equation
y = x2 + ax + b,
where a and b are constants.
Given that the minimum point of C has coordinates (−2, 5), find the values of a and b.
dy/dx = 2x+a
this=0 at minimum point, so a=-2x, and x=-2 (given) so a=4

y =x^2 +4x +b

This = 5 when x=-2 so

5 = 4 - 8 + b

b=9

Aitch
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Aitch
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(Original post by Aitch)
dy/dx = 2x+a
this=0 at minimum point, so a=-2x, and x=-2 (given) so a=4

y =x^2 +4x +b

This = 5 when x=-2 so

5 = 4 - 8 + b

b=9

Aitch
[Puts x^2 +4x+9 into faithful Texas friend. Looks OK.
Aitch]
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roff
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#8
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For the first question at the top of this thread...

would the sum therefore be 720?
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TheWolf
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#9
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Ive got 987

n=21
a=27
d=2

21/2(54+40) = 987
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roff
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#10
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gah, sorry, silly mistake, thanks
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