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Question
If f : R → R is defined by f(x) = x2, write f−1 (25)
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Solution
Let f−1 (25) =x ... (1)
⇒ f (x) = 25
⇒ x2 = 25
⇒ x2 − 25 = 0
⇒ (x−5) (x+5) = 0
⇒ x = ±5
⇒ f−1 (25) = {−5, 5} [from (1)]
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