On donne la fonction suivante :

f(x) = 4x² - 5 

f(3) = 4x3² - 5
f(3) = 4x9 - 5
f(3) = 36 - 5
f(3) = 31.

f(-1) = 4x(-1)² - 5
f(-1) = 4x1 - 5
f(-1) = 4 - 5
f(-1) = -1.

f(1/2) = 4x(1/2)² - 5
f(1/2) = 4x1/4 - 5
f(1/2) = 1 - 5 
f(1/2) = -4.

- 5 = 4 x x² - 5
- 5 + 5 = 4 x x² -5 +5
0 = 4 x x²
x = 0