C1 Question simple

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?

Reply 1

r2they

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

Reply 2

El Stevo

11

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

Reply 3

Aitch

2

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

Reply 4

Mushu

OP

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.

Reply 5

Aitch

2

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.