You'll first triangle. To do this, draw a line and then duplicate it. Rotate the new line exactly 60 degrees and snap the ends of the two lines together. Now repeat this process with a third line to complete the triangle.
Select the entire triangle and choose Modify, Group so that it doesn't cut away from other shapes when you stack them.
Now, because I don't want the circles to eat away at each other yet, select the Oval tool and turn on Object Drawing. Draw a circle that's noticeably larger than the triangle.
Use the Selection tool and select the circle; then make two copies.
Drag each circle by their centers and snap them to the three corners of the triangle.
Select all three circles and via the Properties panel, change the fill to "no fill" (the diagonal red line).
Next, delete the triangle. There are several ways to select the triangle so it's easy to delete: carefully click just the triangle; send all the circles to the back (Modify, Arrange, Send to Back); select all three circles and cut then paste them back after you delete the triangle; or, use the marquee technique to select just the triangle (though you may need to make sure Edit, Preferences, General "Contact-sensitive Selection and Lasso tools" is unchecked).
With the three circle outlines we need to turn them back into a shape to fill each segment. I prefer to just select all three and choose Modify, Break Apart. (Using Modify, Combine Shapes, Union is fine but then you'll need to enter the Drawing Object to fill each part with a unique color.)
Now simply use the bucket tool and fill in the colors (Red, Green, Blue for the large parts; Cyan, Magenta, Yellow for the overlapping parts or vice versa).