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Best Answer: Hey there! The upside down U or ∩ means the intersection of two sets. The intersection of two sets means that the elements of one set is common with the elements of another set. Constructing a Venn diagram is always useful for problems like these. The intersection of ... - read more

Explore This Topic: What does an upside down triangle mean in maths notation? The 'upside down' triangle symbol is the (greek?) letter Nabla. Nabla means the gradient. - read more

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