y=ax+b
Prosta AB :
5=a·2+b
-2=a·(-4)+b
2a+b=5
-4a+b=-2 |·(-1)
2a+b=5
4a-b=2
+-----------
6a=7 |:6
a=7/6
-4·7/6+b=-2
b=8/3
y=7/6x+8/3
Prosta CD :
y=7/6x+b
2=7/6·9+b
2=7/2·3+b
-b=21/2-2
-b=17/2
b=-8 1/2
y=7/6x-8 1/2
Prosta BC :
-2=a·(-4)+b
2=a·9+b
-4a+b=-2
9a+b=2 |·(-1)
-4a+b=-2
-9a-b=-2
+-----------
-13a=-4 |:(-13)
a=4/13
-4·4/13+b=-2
b=-10/13
y=4/13x-10/13
Prosta AD :
y=4/13x+b
5=4/13·2+b
5=8/13+b
-b=8/13-5
-b=-57/13
b=4 5/13
y=4/13x+4 5/13
Proste CD i AD :
7/6x-8 1/2=4/13x+4 5/13
7/6x-17/2=4/13x+57/13 |·78
91x-663=24x+342
91x-24x=342+663
67x=1005 |:67
x=15
y=7/6·15-8 1/2
y=7/2·5-17/2
y=35/2-17/2
y=9
y=4/13·15+4 5/13
y=60/13+57/13
y=117/13
y=9
Punkt D ma współrzędne :
D(15,9)
Odp. D
