3. а) √(x + 4) = 7 |^2

= x + 4 = 49

x = 49 - 4 = 45

x = 45

б) √x = 20 - x | ^2

x = 400 − 40x + x^​2

x − 400 + 40x − x^​2​​ = 0

41x − 400 − x^2​​ = 0

(x − 25)(x − 16) = 0

x = 25; 16

25 не подходит.

x = 16

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