Add pythagorean theorem and unit test

src/main/scala/Mathematics/PythagoreanTheorem.scala

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+package Mathematics
+
+object PythagoreanTheorem {
+
+    /** Returns two dimension distant */
+    def distance(x: Double, y: Double): Double = {
+      Math.sqrt(Math.pow(x,2) + Math.pow(y,2)) 
+    }
+}

src/test/scala/Mathematics/PythagoreanTheoremSpec.scala

@@ -0,0 +1,11 @@
+package Mathematics
+
+import org.scalatest.flatspec.AnyFlatSpec
+
+class PythagoreanTheoremSpec extends AnyFlatSpec {
+
+  "Pythagorean Theorem 1" should "output the correct distant" in {
+    assert(PythagoreanTheorem.distance(3,4) === 5)
+  }
+
+}