Comment faire la suite?

f(√2) = (5√2 - 7)(5√2 + 1)
f(√2) = (5√2)² + 5√2 - (7 x 5)√2 - 7
f(√2) = 50 + 5√2 - 35√2 - 7
f(√2) = 43 - 30√2