Entire triangle has to be reshaped (8)

I believe the answer is:

integral

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'entire' is the definition.
(I know that entire can be written as integral)

'triangle has to be reshaped' is the wordplay.
'triangle' anagrams to 'INTEGRAL'.
Though, I am not sure how this is indicated.

Can you help me to learn more?

(Other definitions for integral that I've seen before include "Of part necessary to the completeness of a whole" , "form whole" , "Inbuilt, essential" , "Belonging as an essential part" , "Basic" .)

I've seen this clue in The Globe and Mail.

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