Prime's slides

My first slide

#include <iostream>
using namespace std;
int main()
{
  cout << "hello world" << endl;
  return 0;
}

#This is markdown
>> Enjoy it.

a,b=map(int,raw_input().split())
print a+b

The code

\sum_{i=a}^{b} {i \times f(i)}

\sum ​ i = a ​ b ​ ​ i \times f (i)

Math

\sum_{k=1}^\infty \frac{x^n}{n!} =\int_0 ^\infty e^x

\sum ​ k = 1 ​ \infty ​ ​ \frac{​ x ​ n ​ ​ ​ ​}{​ n ! ​} = \int ​ 0 ​ \infty ​ ​ e ​ x ​ ​

f(x) = \int_{-\infty}^\infty \hat f(\xi)\,e^{2 \pi i \xi x} \,d\xi

f (x) = \int ​ - \infty ​ \infty ​ ​ ​ f ​^​ ​ (ξ) e ​ 2 π i ξ x ​ ​ d ξ

How to write a matrix on Katex?

Who can tell me?