Crossword Genius

Partial text remains source for mathematical values (7)

Ross

I believe the answer is:

extrema

I'm a little stuck... Click here to teach me more about this clue!

'mathematical values' is the definition.
Although both the answer and definition are plural nouns, I can't understand how one could define the other.

'partial text remains source' is the wordplay.
'partial' indicates a hidden word.
'EXTREMA' can be found hidden inside 'text remains source'.

'for' is the link.

Can you help me to learn more?

(Another definition for extrema that I've seen is " Furthest points".)

I've seen this clue in The Guardian.
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