bonjour,
-t² + 20t + 69 -120 ≥ 0
-t² + 20t - 51 ≥ 0 (1)
Δ = (20²) - 4 x (-1) x (-51) = 400 - 204 = 196 = 14²
t' = (-20-14) / 2x(-1) = -34/-2 = 17
t'' = (-20+14) / 2x(-1) = -6 / (-2) = 3
(1) => -1 x (t-17) (t-3) ≥ 0
t-17 ≥ 0 => t ≥ 17
t-3 ≥ 0 => t ≥ 3
tableau de signes
t -∞ 3 17 ∞
t-17 - - +
t-3 - + +
-1 ( ) ( ) - + -
je te laisse conclure
:)
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bonjour,
-t² + 20t + 69 -120 ≥ 0
-t² + 20t - 51 ≥ 0 (1)
Δ = (20²) - 4 x (-1) x (-51) = 400 - 204 = 196 = 14²
t' = (-20-14) / 2x(-1) = -34/-2 = 17
t'' = (-20+14) / 2x(-1) = -6 / (-2) = 3
(1) => -1 x (t-17) (t-3) ≥ 0
t-17 ≥ 0 => t ≥ 17
t-3 ≥ 0 => t ≥ 3
tableau de signes
t -∞ 3 17 ∞
t-17 - - +
t-3 - + +
-1 ( ) ( ) - + -
je te laisse conclure
:)