### Question:
LinearAlgebraUtils { public static double[] solve22(double[][] A, double[] y) throws IllegalArgumentException { double[] result = new double[2]; if (A[0].length != 2 || A.length != 2) { throw new IllegalArgumentException("solve22: input: size of A not 22."); } if (y.length != 2) { throw new IllegalArgumentException("solve22: input: size y not 2x1."); } result[1] = (y[0] - ((A[0][0] / A[1][0]) * y[1])) / (A[0][1] - ((A[0][0] * A[1][1]) / A[1][0])); result[0] = (y[0] - A[0][1] * result[1]) / A[0][0]; return result; }  static double[] solve22(double[][] A, double[] y); static double[] solve33(double[][] A, double[] rhs); static DoubleMatrix absMatrix(DoubleMatrix inMatrix); static double[][] absMatrix(double[][] inMatrix); static DoubleMatrix matrixPower(DoubleMatrix data, double scalar); static double[][] matrixPower(double[][] inMatrix, double scalar); static void invertChol_inplace(double[][] inMatrix); static double[][] invertChol(double[][] inMatrix); static void invertChol_inplace(DoubleMatrix inMatrix); static DoubleMatrix invertChol(DoubleMatrix inMatrix); static ComplexDoubleMatrix dotmult(ComplexDoubleMatrix A, ComplexDoubleMatrix B); static void dotmult_inplace(ComplexDoubleMatrix A, ComplexDoubleMatrix B); static void fliplr_inplace(DoubleMatrix A); static DoubleMatrix matTxmat(DoubleMatrix matrix1, DoubleMatrix matrix2); static ComplexDoubleMatrix matTxmat(ComplexDoubleMatrix matrix1, ComplexDoubleMatrix matrix2); static void wshift_inplace(DoubleMatrix inVector, int n); static DoubleMatrix wshift(DoubleMatrix inMatrix, int n); static void setdata(DoubleMatrix outMatrix, Window outWin, DoubleMatrix inMatrix, Window inWin); static void setdata(ComplexDoubleMatrix outMatrix, Window outWin, ComplexDoubleMatrix inMatrix, Window inWin); static void setdata(ComplexDoubleMatrix outMatrix, ComplexDoubleMatrix inMatrix, Window inWin); static void setdata(DoubleMatrix outMatrix, DoubleMatrix inMatrix, Window inWin); static void chol_inplace(double[][] inMatrix); static void chol_inplace(DoubleMatrix inMatrix); static void invert_inplace(double[][] inMatrix); static double[][] invert(double[][] inMatrix); static void invert_inplace(DoubleMatrix inMatrix); static DoubleMatrix invert(DoubleMatrix inMatrix); static void arrangeCholesky_inplace(DoubleMatrix inMatrix); static void arrangeCholesky_inplace(double[][] inArray);  }### Answer:
@Test public void testSolve22() throws Exception { double[] SOL_22_ACTUAL = LinearAlgebraUtils.solve22(A_PASCAL_22.toArray2(), X_22); Assert.assertArrayEquals(SOL_22_EXPECTED, SOL_22_ACTUAL, DELTA); }