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f(1)=3, f(2)=10 f(n)=4+2f(n-1)-f(n-2) We are asked to write the first five terms of f(n). Let's do it!
n | f(n-2) | f(n-1) | 4+2f(n-1)-f(n-2) | f(n)=4+2f(n-1)-f(n-2) |
---|---|---|---|---|
1 | - | - | - | f(1)=3 |
2 | - | - | - | f(2)=10 |
3 | f(1)= 3 | f(2)= 10 | 4+2( 10)- 3= 21 | f(3)= 21 |
4 | f(2)= 10 | f(3)= 21 | 4+2( 21)- 10= 36 | f(4)= 36 |
5 | f(3)= 21 | f(4)= 36 | 4+2( 36)- 21= 55 | f(5)= 55 |
We will use patterns between consecutive data pairs to determine what type of function best models the given values from Part A. The differences of consecutive f-values are called first differences. The differences of consecutive first differences are called second differences.
Remember that in all cases the differences of consecutive n-values need to be constant! Let's analyze the table of values and compute the first differences.
Since the first differences are not constant, the sequence cannot be modeled by a linear function. Next we will check the second differences.
Since the second differences are constant, the sequence can be modeled by a quadratic function.
(I), (II), (III):Calculate power and product
(I), (II), (III):Rearrange equation
(I):LHS-a=RHS-a
(I):LHS-b=RHS-b
(I), (II):c= 3-a-b
(II), (III): Add and subtract terms
(II), (III): LHS-3=RHS-3
(II):LHS-3a=RHS-3a
(III):b= 7-3a
(III):Distribute 2
(III):Subtract terms
(III):LHS-14=RHS-14
(III):.LHS /2.=.RHS /2.
(II):a= 2
(II):Multiply
(II):Subtract terms
(I):a= 2, b= 1
(I):Subtract terms
Substitute expressions
Distribute -1
(a-b)^2=a^2-2ab+b^2
Distribute 2 & Distribute - 2
Add and subtract terms
Distribute 2
Add and subtract terms
LHS-n=RHS-n
LHS-2n^2=RHS-2n^2