add cos function

src/exponent.h

@@ -3,6 +3,5 @@
 
 double p(double exp, double base);
 double powerD(double exp, double base);
-double absD(double x);
 
 #endif // exponent.h

src/reihen.c

@@ -42,7 +42,6 @@ double pi(double eps){
 }
 
 double sinD(double degrees){
-
     if (degrees>=360.0){
         degrees = squashDegreesTo360(degrees);
     }
@@ -61,3 +60,23 @@ double sinD(double degrees){
     }
     return sum;
 }
+
+double cosD(double degrees){
+    if (degrees>=360.0){
+            degrees = squashDegreesTo360(degrees);
+    }
+    double sum = 0.0;
+    double currvalue;
+    double radian = radians(degrees);
+    double power;
+    unsigned long long faculty;
+    for (int i = 0; i <= 9; i++)
+    {
+        currvalue = 1.0;
+        currvalue *= powerD(2*i, radian);
+        currvalue /= fac(2*i);
+        if(i%2==0) sum += currvalue;
+        else sum -= currvalue;
+    }
+    return sum;
+}

src/reihen.h

@@ -6,5 +6,6 @@ double euler();
 double pi();
 double radians(double degrees);
 double sinD(double degrees);
+double cosD(double degrees);
 
 #endif // reihen.h