The easiest way to do this is to multiple 7 and 3, which gives you 21. Julie will spend $21 on the gifts.
Answer:
(a) The sum of the previous term and 9
(b) 36, 45, 54
Step-by-step explanation:
Given
Sequence: Arithmetic Progression

Solving (a): Describe the relationship in each term
First, we calculate the common difference (d)
In arithmetic progression:

Take n as 2


Where



<em>The relationship is: The sum of the previous term and 9</em>
Solving (b): The next three terms
As said in (a) each term is derived from a sum of 9 and the previous term
So, we have:



Hence, the next three terms are: 36, 45 and 54
Since
, we can rewrite the integral as

Now there is no ambiguity about the definition of f(t), because in each integral we are integrating a single part of its piecewise definition:

Both integrals are quite immediate: you only need to use the power rule

to get
![\displaystyle \int_0^11-3t^2\;dt = \left[t-t^3\right]_0^1,\quad \int_1^4 2t\; dt = \left[t^2\right]_1^4](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Cint_0%5E11-3t%5E2%5C%3Bdt%20%3D%20%5Cleft%5Bt-t%5E3%5Cright%5D_0%5E1%2C%5Cquad%20%5Cint_1%5E4%202t%5C%3B%20dt%20%3D%20%5Cleft%5Bt%5E2%5Cright%5D_1%5E4)
Now we only need to evaluate the antiderivatives:
![\left[t-t^3\right]_0^1 = 1-1^3=0,\quad \left[t^2\right]_1^4 = 4^2-1^2=15](https://tex.z-dn.net/?f=%5Cleft%5Bt-t%5E3%5Cright%5D_0%5E1%20%3D%201-1%5E3%3D0%2C%5Cquad%20%5Cleft%5Bt%5E2%5Cright%5D_1%5E4%20%3D%204%5E2-1%5E2%3D15)
So, the final answer is 15.
Fyi I didn't find this on google or anything I did the calculation on my computer and yes this is correct...
If it's wrong I'm sorry...
I think it should be an= 49x3^(n-1)