Added area of a triangle.

src/main/java/com/thealgorithms/maths/Area.java

@@ -1,4 +1,4 @@
 package com.thealgorithms.maths;
 
 /**
  * Find the area of various geometric shapes
@@ -233,3 +233,22 @@
         return Math.PI * radius * (radius + Math.pow(height * height + radius * radius, 0.5));
     }
 }
+
+/**
+* Calculate the surface area of a pyramid with a square base.
+*
+* @param sideLength side length of the square base
+* @param slantHeight slant height of the pyramid
+* @return surface area of the given pyramid
+*/
+public static double surfaceAreaPyramid(final double sideLength, final double slantHeight) {
+if (sideLength <= 0) {
+throw new IllegalArgumentException("Must be a positive sideLength");
+}
+if (slantHeight <= 0) {
+throw new IllegalArgumentException("Must be a positive slantHeight");
+}
+double baseArea = sideLength * sideLength;
+double lateralSurfaceArea = 2 * sideLength * slantHeight;
+return baseArea + lateralSurfaceArea;
+}