\documentclass[a4paper,landscape]{article}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}
\usetikzlibrary{calc,fadings,decorations.pathreplacing}
%% helper macros
\usepackage[cp1251]{inputenc}
\usepackage{cmap} % для корректной генерации русского текста в PDF
\usepackage{mathtext} % русские буквы в формулах
\usepackage[T2A]{fontenc}
\usepackage[russian]{babel}
\usepackage{amssymb}
\usepackage{pgfplots}
\usepackage{amsmath}
\usepackage{gensymb}
\usepackage{graphicx}
\usepackage{indentfirst} % отступ первого абзаца
\usepackage{calc}
\usepackage{icomma} % правильная десятичная запятая
\usetikzlibrary{snakes}
\usetikzlibrary{patterns}
\usetikzlibrary {calc}
\usepackage{geometry}
%\geometry{papersize={ 20.5 cm, 12 cm }}
\geometry{left=5cm}
%\geometry{right=0cm}
\geometry{top=2cm}
%\geometry{bottom=0.1cm}
\tikzstyle{spring}=[line width=0.8,blue!7!black!80,snake=coil,segment amplitude=5,segment length=5,line cap=round]

\def\textto{Лист необходимо сдать вместе со своими решениями!}
\begin{document}
\thispagestyle{empty}
\pgfkeys{/pgf/number format/.cd,1000 sep={}}
\begin{tikzpicture}
%\draw (0,0) -- ({atan(1)}:{sqrt(2)+2} );
\draw (10, 12.5) node{\textto};
\draw (10, -3) node{\textto};
\begin{axis}[
    xmin = 985, xmax = 1250,
    ymin = 0, ymax = 49.0,
    xtick distance = 50,
    ytick distance = 5,
    grid = both,
    axis x line*=bottom,
    axis y line*=left,
    minor tick num = 4,
    major grid style = {lightgray},
    minor grid style = {lightgray!25},
    width = 19.5 cm,
    height = 12 cm]
    \addplot[
        domain = 985:1250,
        samples = 100,
        smooth,
        thick,
        blue,
    ] {5+40*exp(-(x-1125)*(x-1125)/300))};
%   \addplot[domain = 1010:1250, samples = 100, smooth, thick, gray, ] {-273 + 2.67 + 0.267*x};
\end{axis}
\draw (18.5, 0.2) node{\large $h,$ м};
\draw (-0.5, 10.5) node{\large $t, {\degree}$C};
%\draw[fill] (3.12, 1.06) circle(0.05 cm) node[yshift = 0.5 cm]{\Large $A$};
%\draw[fill] (8.54, 5.6) circle(0.05 cm) node[xshift = - 0.5 cm]{\Large $B$};
%\draw[fill] (10.18, 6.98) circle(0.05 cm) node[xshift = 0.5 cm]{\Large $C$};
\end{tikzpicture}
\end{document}