Add/linear equation

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

@@ -0,0 +1,27 @@
+package com.thealgorithms.maths;
+
+/**
+ * Solves linear equations of the form ax + b = 0.
+ *
+ * @see <a href="https://en.wikipedia.org/wiki/Linear_equation">Linear equation (Wikipedia)</a>
+ */
+public final class LinearEquation {
+
+    private LinearEquation() {
+    }
+
+    /**
+     * Solves the equation ax + b = 0 and returns the value of x.
+     *
+     * @param a the coefficient of x, must not be zero
+     * @param b the constant term
+     * @return the value of x that satisfies the equation
+     * @throws IllegalArgumentException if a is zero
+     */
+    public static double solve(final double a, final double b) {
+        if (a == 0) {
+            throw new IllegalArgumentException("Coefficient 'a' must not be zero");
+        }
+        return -b / a;
+    }
+}

src/test/java/com/thealgorithms/maths/LinearEquationTest.java

@@ -0,0 +1,35 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertAll;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+class LinearEquationTest {
+
+    @Test
+    void testSolveBasic() {
+        assertEquals(3.0, LinearEquation.solve(2, -6));
+    }
+
+    @Test
+    void testSolveNegativeResult() {
+        assertEquals(-5.0, LinearEquation.solve(1, 5));
+    }
+
+    @Test
+    void testSolveWithZeroB() {
+        assertEquals(0.0, LinearEquation.solve(4, 0), 1e-9);
+    }
+
+    @Test
+    void testSolveWithNegativeA() {
+        assertEquals(3.0, LinearEquation.solve(-3, 9));
+    }
+
+    @Test
+    void testAllIllegalInput() {
+        assertAll(() -> assertThrows(IllegalArgumentException.class, () -> LinearEquation.solve(0, 5)), () -> assertThrows(IllegalArgumentException.class, () -> LinearEquation.solve(0, 0)), () -> assertThrows(IllegalArgumentException.class, () -> LinearEquation.solve(0, -3)));
+    }
+}