Verified answer

y = -8 + 5√(5x - 1)

y + 8 = 5√(5x - 1)

(y + 8)/5 = √(5x - 1)

(y + 8)²/25 = (5x - 1)

(y + 8)²/25 + 1 = 5x

(y² + 16y + 64)/25 + 25/25 = 5x

(y² + 16y + 89)/125 = x

f ֿ¹ (x) = (x² + 16x + 89)/125

f (x) = -8 + 5√(5x − 1)

x = -8 + 5√(5y − 1)

x + 8 = 5√(5y − 1)

√(5y − 1) = (x + 8)/5

5y − 1 = (x + 8)²/25

5y = (x + 8)²/25 + 1

y = (x + 8)²/125 + 5

y = (x² + 16x + 64 + 625)/125

f ֿ¹ (x) = (x² + 16x + 689)/125