diff --git a/.classpath b/.classpath
new file mode 100644
index 0000000..287dc14
--- /dev/null
+++ b/.classpath
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER">
+		<attributes>
+			<attribute name="module" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry kind="con" path="org.eclipse.jdt.junit.JUNIT_CONTAINER/5"/>
+	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="output" path="bin"/>
+</classpath>
diff --git a/.gitignore b/.gitignore
index b0cbf6e..85e6efb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@
 # Mac OS System
 .DS_Store*
 ._*
+/bin/
diff --git a/.project b/.project
new file mode 100644
index 0000000..02992da
--- /dev/null
+++ b/.project
@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>Simple-Java-Calculator</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+	</natures>
+</projectDescription>
diff --git a/src/simplejavacalculator/Calculator.java b/src/simplejavacalculator/Calculator.java
index 18ad91c..9348f06 100644
--- a/src/simplejavacalculator/Calculator.java
+++ b/src/simplejavacalculator/Calculator.java
@@ -23,7 +23,7 @@ public enum BiOperatorModes {
     }
 
     public enum MonoOperatorModes {
-        square, squareRoot, oneDividedBy, cos, sin, tan ,log , rate, abs
+        square, squareRoot, oneDividedBy, cos, sin, tan, inverseCos ,log , rate, abs
     }
 
     private Double num1, num2;
@@ -109,6 +109,9 @@ public Double calculateMono(MonoOperatorModes newMode, Double num) {
 
             return Math.tan(Math.toRadians(num));
         }
+        if(newMode == MonoOperatorModes.inverseCos) {
+        	return Math.toDegrees(Math.acos(num));
+        }
         if (newMode == MonoOperatorModes.log) {
             return log10(num);
         }
diff --git a/src/simplejavacalculator/UI.java b/src/simplejavacalculator/UI.java
index 8e9cc4a..79e0f7f 100644
--- a/src/simplejavacalculator/UI.java
+++ b/src/simplejavacalculator/UI.java
@@ -51,7 +51,7 @@ public class UI implements ActionListener {
    private final JTextArea text;
    private final JButton but[], butAdd, butMinus, butMultiply, butDivide,
       butEqual, butCancel, butSquareRoot, butSquare, butOneDividedBy,
-      butCos, butSin, butTan, butxpowerofy, butlog, butrate, butabs, butBinary;
+      butCos, butSin, butTan, butInverseCos, butxpowerofy, butlog, butrate, butabs, butBinary;
    private final Calculator calc;
    
    private final String[] buttonValue = {"0", "1", "2", "3", "4", "5", "6",
@@ -99,7 +99,8 @@ public UI() throws IOException {
       butOneDividedBy = new JButton("1/x");      
       butCos = new JButton("Cos");      
       butSin = new JButton("Sin");      
-      butTan = new JButton("Tan");      
+      butTan = new JButton("Tan");
+      butInverseCos = new JButton("Cos^-1");
       butxpowerofy = new JButton("x^y");      
       butlog = new JButton("log10(x)");      
       butrate = new JButton("x%");      
@@ -135,6 +136,7 @@ public void init() {
       butCos.setFont(font);
       butSin.setFont(font);
       butTan.setFont(font);
+      butInverseCos.setFont(font);
       butxpowerofy.setFont(font);
       butlog.setFont(font);
       butrate.setFont(font);
@@ -184,6 +186,7 @@ public void init() {
       panelSub7.add(butCos);
       panelSub7.add(butSin);
       panelSub7.add(butTan);
+      panelSub7.add(butInverseCos);
       panel.add(panelSub7);
       
       panelSub8.add(butlog);
@@ -205,6 +208,7 @@ public void init() {
       butCos.addActionListener(this);
       butSin.addActionListener(this);
       butTan.addActionListener(this);
+      butInverseCos.addActionListener(this);
       butxpowerofy.addActionListener(this);
       butlog.addActionListener(this);
       butrate.addActionListener(this);
@@ -279,6 +283,9 @@ public void actionPerformed(ActionEvent e) {
 
          if (source == butTan)
             writer(calc.calculateMono(Calculator.MonoOperatorModes.tan, reader()));
+         
+         if (source == butInverseCos)
+             writer(calc.calculateMono(Calculator.MonoOperatorModes.inverseCos, reader()));
 
          if (source == butlog)
             writer(calc.calculateMono(Calculator.MonoOperatorModes.log, reader()));
diff --git a/src/simplejavacalculatorTest/CalculatorTest.java b/src/simplejavacalculatorTest/CalculatorTest.java
index 1ea20f7..67cafcd 100755
--- a/src/simplejavacalculatorTest/CalculatorTest.java
+++ b/src/simplejavacalculatorTest/CalculatorTest.java
@@ -97,6 +97,12 @@ void CalculateMonoTanTest() {
 		Assertions.assertEquals(1.0, calculator.calculateMono(Calculator.MonoOperatorModes.tan, java.lang.Math.PI / 4), 0.0000000001);
 	}
 	
+	@Test
+	void CalculateMonoInverseCosTest() {
+		Calculator calculator = new Calculator();
+		Assertions.assertEquals(90.0, calculator.calculateMono(Calculator.MonoOperatorModes.inverseCos, 0.0), 0.0000000001);
+	}
+	
 	@Test
 	void CalculateMonoLogTest() {
 		Calculator calculator = new Calculator();