Essa foi minha resolução para o esquadro
<!DOCTYPE html>
<html lang="pt-br">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>esquadrot</title>
</head>
<body>
<canvas width="600" height="400"></canvas>
<script>
var tela = document.querySelector('canvas');
var pincel = tela.getContext('2d');
pincel.fillStyle = 'lightgrey';
pincel.fillRect(0, 0, 600, 400);
pincel.fillStyle = 'black'
pincel.beginPath ();
pincel.moveTo(50,50);
pincel.lineTo(50, 400)
pincel.lineTo(400, 400)
pincel.fill();
pincel.fillStyle = 'white'
pincel.beginPath ();
pincel.moveTo(100,175);
pincel.lineTo(100, 350)
pincel.lineTo(275, 350)
pincel.fill();
</script>
</body>
</html>
