documentclass{article}
usepackage{pstricks}
usepackage{pst-node}

usepackage{FiraMono}
usepackage[T1]{fontenc}


begin{document}
    SCALENE TRIANGLE
begin{pspicture}(0,0)
    pspolygon(1,1)(3,4)(9,1)   %triangle
    psline[linestyle=dashed](3,4)(3,1) %height
    pspolygon(3,1)(3,1.2)(3.2,1.2)(3.2,1)  %right angle
    uput{0.1}[180](1,1){A}
    uput{0.1}[90](3,4){B}
    uput{0.1}[0](9,1){C}
    uput{0.2}[0](6,2.5){a}
    uput{0.2}[270](5,1){b}
    uput{0.2}[180](2,2.5){c}
    uput{0.2}[0](3,2.5){h}
end{pspicture}
    $$area = sqrt{s(s-a)(s-b)(s-c)},quad s = frac{(a+b+c)}{2}$$
end{document}