Drawing an equilateral triangle requires a bit of math to calculate the 'height' of the triangle, which will allow us to figure out the y coordinate.
In this example, each side is 300 pixels in length. The equilateral triangle is composed of 2 similar right-angled triangles.
From Pythagoras we know the hypotenuse is the square root of the sum of the squares of the other 2 sides.
We have 2 sides of the right-angled triangle:
So the height (long side) of this triangle is √(300² - 150²), which is about 259.8.
Since our bottom side is placed at y=480, the apex y will be at 480-259.8 = 220.19. Recall that SVG coordinates start at the top-left (0,0).