Update Unit 2: Sequences, Series, and Financial Applications.md

Grade 10/Math/MCR3U7/Unit 2: Sequences, Series, and Financial Applications.md

@@ -16,7 +16,7 @@
 **infinite series**: infinite series have **infinite** number of terms.
 - eg. $`1 + 2 + 3 + \cdots`$
 
-Terms in a sequence are numbered with subscripts: $~t_1, t_2, t_3, \cdots t_n`$ where $`t_n`$is the general or $`n^{th}`$ term.
+Terms in a sequence are numbered with subscripts: $`t_1, t_2, t_3, \cdots t_n`$ where $`t_n`$is the general or $`n^{th}`$ term.
 
 **Series**: A series is the sum of the terms of a sequence.
 
@@ -129,7 +129,7 @@ $`\large I = Prt`$
 - $`r`$ is the annual interest rate expressed as a decimal (the percent is $`1 - r`$)
 - $`t`$ is the time in years.
 
-- This interest is calculated from the original amount each time. (eg. if you had $$`100`$, and your interest is $`1\%`$, your interest will be a constant $$`1`$ each time.)
+- This interest is calculated from the original amount each time. (eg. if you had $100, and your interest is 1\%, your interest will be a constant $1 each time.)
 
 
 The total amount would be $`P + I`$.
@@ -167,4 +167,12 @@ Since it is basically the summation of a geometric sequence, we can apply the ge
 ```math
 \large
 FV = \frac{R[(1+\frac{r}{n})^n - 1]}{\frac{r}{n}}
+```
+
+## Present Value Annuities
+The **Present Value** of an annuity is today's value of having equally spaced payments or withdrawals of money sometime in the future.
+
+```math
+\large
+PV = \frac{R[1 -(1+\frac{r}{n})^{-n}]}{\frac{r}{n}}
 ```