A(8;-2), B(6;-5)
y=ax+b
-2=a·8+b
-5=a·6+b
8a+b=-2
6a+b=-5 |·(-1)
8a+b=-2
-6a-b=5
+------------
2a=3 |:2
a=3/2
8·3/2+b=-2
12+b=-2
b=-2-12
b=-14
y=3/2x-14
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S=((xa+xb)/2;(ya+yb)/2)
S=((8+6)/2;(-2-5)/2)
S=(14/2;(-7/2)
S=(7;-3 1/2)
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a=3/2
3/2·a₂=-1
a₂=-2/3
y=-2/3x+b
-3 1/2=-2/3·7+b
-3 1/2=-4 2/3+b
-b=-4 2/3+3 1/2
-b=-4 4/6+3 3/6
-b=-1 1/6
b=1 1/6
y=-2/3a+1 1/6