bonjour
f(x) = -5x² + 15x + 25 ; définie sur R
1)
f'(x) = -2*5x + 15*1
= -10x + 15
2) ↗ ↘
-10x + 15 = 0 <=> 10x = 15
x = 15/10
x = 3/2
-10x + 15 > 0 <=> -10x + 15 > 0
-10x > - 15
x < 3/2
-10x + 15 < 0 <=> x > 3/2
3)
tableau des variations
x -∞ 3/2 +∞
-10x + 15 + 0 -
f(x) 25
↗ ↘
-∞ +∞
