<canvas width="600" height="400"></canvas>
<script>
var tela = document.querySelector('canvas');
var pincel = tela.getContext('2d');
pincel.fillStyle = "green";
pincel.fillRect(0,0,600,400);//cria retangulo cinza do tamanho do canvas
pincel.beginPath();
pincel.fillStyle="yellow";
pincel.moveTo(50, 200);
pincel.lineTo(300,25);
pincel.lineTo(550,200);
pincel.moveTo(50, 200);
pincel.lineTo(300,375);
pincel.lineTo(550,200);
pincel.fill();
pincel.fillStyle="darkblue";
pincel.beginPath();
pincel.arc(300, 200, 100, 0, 2*3.14);
pincel.fill();
</script>
