user236501 - 1 year ago 72

Java Question

I know Math.sin() can work but I need to implement it myself using factorial(int) i have a factorial method already below are my sin method but i can't get the same result as

`Math.sin()`

`public static double factorial(double n) {`

if (n <= 1) // base case

return 1;

else

return n * factorial(n - 1);

}

public static double sin(int n) {

double sum = 0.0;

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

if (i % 2 == 0) {

sum += Math.pow(1, i) / factorial(2 * i + 1);

} else {

sum += Math.pow(-1, i) / factorial(2 * i + 1);

}

}

return sum;

}

Answer Source

You should use the Taylor series. A great tutorial here

I can see that you've tried but your sin method is incorrect

```
public static sin(int n) {
// angle to radians
double rad = n*1./180.*Math.PI;
// the first element of the taylor series
double sum = rad;
// add them up until a certain precision (eg. 10)
for (int i = 1; i <= PRECISION; i++) {
if (i % 2 == 0)
sum += Math.pow(rad, 2*i+1) / factorial(2 * i + 1);
else
sum -= Math.pow(rad, 2*i+1) / factorial(2 * i + 1);
}
return sum;
}
```

A working example of calculating the sin function. Sorry I've jotted it down in C++, but hope you get the picture. It's not that different :)