JSFiddle - React, Tailwind, and code Playground

HTML

<canvas id="equ" width="300" height="300"></canvas>

JavaScript

var ax=0;
var ay=0;
var bx=0;
var by=150;

var dx=bx-ax
var dy=by-ay;
var dangle = Math.atan2(dy, dx) - Math.PI / 3;
var sideDist = Math.sqrt(dx * dx + dy * dy);

var cx = Math.cos(dangle) * sideDist + ax;
var cy =  Math.sin(dangle) * sideDist + ay;

var canvas = document.getElementById('equ');
var ctx = canvas.getContext('2d');

ctx.beginPath();  
ctx.moveTo(ax,ay);  
ctx.lineTo(bx,by);  
ctx.lineTo(cx,cy);  

ctx.fill();