matlab微积分编程问题

编程求两种情形下对应x点处二阶导数值，函数文件第一行格式已确定

syms a x y;
y = a * exp(x) / sqrt(a + x^2);

% a = 2, x = 3a
a1 = 2;
x1 = 3 * a1;
y1 = subs(y, {a, x}, {a1, x1});
diff_y1 = diff(y, x);
diff2_y1 = diff(diff_y1, x);
result1 = eval(subs(diff2_y1, x, x1));

% a = 3, x = 2a
a2 = 3;
x2 = 2 * a2;
y2 = subs(y, {a, x}, {a2, x2});
diff_y2 = diff(y, x);
diff2_y2 = diff(diff_y2, x);
result2 = eval(subs(diff2_y2, x, x2));