Fix LaTeX expression in ChebshevT (#393)

Signed-off-by: ErikQQY <[email protected]>

Author: ErikQQY

docs/src/polynomials/chebyshev.md

@@ -7,7 +7,28 @@ end
 ```
 
 
-The [Chebyshev polynomials](https://en.wikipedia.org/wiki/Chebyshev_polynomials) are two sequences of polynomials, `T_n` and `U_n`. The Chebyshev polynomials of the first kind, `T_n`, can be defined by the recurrence relation `T_0(x)=1`, `T_1(x)=x`, and `T_{n+1}(x) = 2xT_n{x}-T_{n-1}(x)`. The Chebyshev polynomioals of the second kind, `U_n(x)`, can be defined by `U_0(x)=1`, `U_1(x)=2x`, and `U_{n+1}(x) = 2xU_n(x) - U_{n-1}(x)`. Both `T_n` and `U_n` have degree `n`, and any polynomial  of  degree `n` may be uniquely written as a linear combination of the polynomials `T_0`, `T_1`, ..., `T_n` (similarly with `U`).
+The [Chebyshev polynomials](https://en.wikipedia.org/wiki/Chebyshev_polynomials) are two sequences of polynomials, ``T_n`` and ``U_n``. The Chebyshev polynomials of the first kind, ``T_n``, can be defined by the recurrence relation:
+
+```math
+T_0(x)=1,\ T_1(x)=x
+```
+
+```math
+T_{n+1}(x) = 2xT_n{x}-T_{n-1}(x)
+```
+
+The Chebyshev polynomioals of the second kind, ``U_n(x)``, can be defined by
+
+```math
+U_0(x)=1,\ U_1(x)=2x
+```
+
+```math
+U_{n+1}(x) = 2xU_n(x) - U_{n-1}(x)
+```
+
+
+Both ``T_n`` and ``U_n`` have degree ``n``, and any polynomial of degree ``n`` may be uniquely written as a linear combination of the polynomials ``T_0``, ``T_1``, ..., ``T_n`` (similarly with ``U_n``).
 
 
 ## First Kind
@@ -16,9 +37,9 @@ The [Chebyshev polynomials](https://en.wikipedia.org/wiki/Chebyshev_polynomials)
 ChebyshevT
 ```
 
-The `ChebyshevT` type holds coefficients representing the polynomial `a_0 T_0 + a_1 T_1 + ... + a_n T_n`.
+The `ChebyshevT` type holds coefficients representing the polynomial ``a_0 T_0 + a_1 T_1 + ... + a_n T_n``.
 
-For example, the basis polynomial `T_4` can be represented with `ChebyshevT([0,0,0,0,1])`.
+For example, the basis polynomial ``T_4`` can be represented with `ChebyshevT([0,0,0,0,1])`.
 
 
 ### Conversion