Hot answers tagged shapes
If you start with the disc in the middle, you know its radius in pixels: R_red. The area A of the disc is A=pi*R_red**2. A is also the area of the green and blue area, respectively. Therefore, the outer radius of the green ring belongs to a disc with area 2*A. R_green = sqrt(2*A/pi)), and consequently R_blue=sqrt(3*A/pi)). So, R_green is sqrt(2) ...
The Shift key constrains proportions. If you start with an oval, it will continue to be an ellipse as you scale it. To turn an ellipse into a circle, or a rectangle into a square, adjust the height and width properties manually (be sure that auto-keyframe is turned off if you don't want to make this part of an animation) so they are the same.
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