Posted by Cassie on Monday, April 20, 2009 at 4:07pm.
your formula can't be right,
try n=3 ---> 2.5(3) + 1.5(3) = 12 not the 15 that are needed.
I do these the following way:
4,8,15,25
the first set of differences between successive terms is 4,7,10
and the second differences are 3,3
so we have a constant difference in the second set, so the function must be quadratic
let it be y = an^2 + bn + c
from you data:
4 = a+b+c
8 = 4a+2b+c
15 = 9a+3b+c
subtract the first two: 4 = 3a + b
subtract the last two : 7 = 5a + b
now subract these two 3 = 2a
a = 3/2
sub into 4 = 3a+b --> b = -1/2
and finally back in the first gives us
c = 3
so y = (3/2)n^2 - n/2 + 3
try it, it works.
Related Questions
Algebra - The pattern is: 4, 8, 15, 25 Is the formula: 2.5n + 1.5n??? If you are...
algebra - Could someone check my work; 1. Generate the first five terms in the ...
math - I know "!" means e.g. 5!=5x4x3x2x1 but how about [3(n+1)!]/[5n...
Exterior angle what am I doing wrong? - Find the measure of the indicated ...
Algebra - Simplify: (4m/5n^2)-(n/2m) A)(8m^2-5n^3)/10n^2m B)(8m^2+5n^3)/10n^2m C...
Geometry - 1.) -9 + 4r = 4r - 3 - 6 2.) 6x - 2x + 8 = x + 5 3.) 4n + 5n + 15 = ...
algebra - What's the solution to 5n+1=5n-1. Please tell me if it's no ...
Quadratic Equations - Ok, I am supposed to find out what the variables are by ...
math - JUSTIFIES A STEP IN THE SOLUTION OF AN EQUATION 4n+(7+n)=52 4n+(n+7)=52 (...
matn - JUSTIFIES A STEP IN THE SOLUTION OF AN EQUATION 4n+(7+n)=52 4n+(n+7)=52 (...
For Further Reading
