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The sum of the first n terms of the sequence 1, 2.25, 3.5... can be found by using the formula ...?
S=n/2 [2+(n=1) x 1.25]
use this formula to find the sum of:
a) the first 5 terms.
b)the first 17 terms
im totally stuck on this problem, i dont even know how to start! can anyone give me any suggestions on how i can go about solving it?! all help appreciated!
thanks soo much.
god, im really sorry, i typed the formula wrong. its meant to be:
S=n/2 [2+(n-1)x1.25]
sorry! :$
3 Answers
- Dennis KLv 41 decade ago
Shouldn't the equation read S = n/2 [2+(n-1) x 1.25?
If you want 5, replace n with 5
If you want 17, replace n with 17
See if you replace n with 1 then it is 1/2[2+(1-1) x 1.25 = 1
replace n with 2 then it is 2/2[2+(2-1) x 1.25 = 3.25
see, that was the sum of the first 2 terms, 1 and 2.25.
put 5 in there and the equation will be 5/2[2+(5-1)x 1.25 = 17.5
check my math
- 1 decade ago
I think the pattern is 1.25 has been added to each number so the next five numbers would be 4.75, 6, 7.25, 8.5, 9.75, 11 and so on
