alternating series sum java help

For my assignment I have to create a program that calculates the following:

x - x^3/3! + x^5/5! - x^7/7! + ..... + - x^n/n!

Where the user inputs the value of x they want to calculate and inputs the value of n for the maximum exponent value (the higher the exponent the user inputs the more accurate the calculation will be).

Here's my attempt to the problem:

Code:

`import java.io.*;`

public class s {

public static void main(String args[]) throws IOException

{

BufferedReader keybd = new BufferedReader(new InputStreamReader(System.in));

double x;

int n;

System.out.print("Input a value for x: ");

x = Double.parseDouble(keybd.readLine());

System.out.print("Input max exponent: ");

n = Integer.parseInt(keybd.readLine());

int factorial=1;

for (int i=2; i<=n; i++) // this for loop finds factorials (ie 5!=120)

{

factorial = factorial * i;

}

int exp=1;

double sum = 0;

for (int i=1; i<=n; i=i+2)

{

sum = sum + (Math.pow(-1,i))*(Math.pow(x,i))/(factorial);

// i don't think I did the factorial part correctly.

// Also I can't get the alternating between positive and negative. it starts with negative because (-1)^1= -1 but the first term of series has to be positive.

}

System.out.println("The result is: " + sum);

}

}

Please help! Thanks!