Odpowiedzi

2009-12-17T14:49:45+01:00
S=180km
V1=x
V2=x+30
t=?
t2=t-1h
v1=190/t ^ v2=180/t2
x=180/t ^ x+30=180:(t-1)
180/t +30 =180:(t-1) /* t
180 + 30t=180t:(t-1) /*t-1
(t-1)180 +30t(t-1)=180t
180t-180 +30t^2 -30t = 180t /-180t
-180 +30t^2 -30t =0
3t^2 -3t -18=0
t^2 -t -6=0
delta =25
pierw. z delty =5
t1=3
t2=-2 (nie nalezy do dziedziny)

v=s/t
v= 180km/3h
v=60km/h

2009-12-17T14:59:51+01:00
Wzór ogólny v*t = s

dane z zadania:
{v*t = 180
{(v+30)*(t−1) = 180
{v = 180/t (podstawiam do drugiego)
{(180/t + 30)(t-1) = 180
{v = 180/t
{180-180/t + 30t-30 = 180|:30
{v = 180/t
{6-6/t-1=6
t²−t−6=0 Δ=25 √Δ=5 t₁=3 t₂-ujemne

v = 180/t
v = 180/3
v = 60 km/h