y=2x+2
(2) A(0,2),B(- 1,0)
M: y=2x+t, then c (-t/2,0)
BC = |- 1-(-t/2)| = | t/2- 1 |
OA=2
s = BC * OA/2 = | t/2- 1 | * 2/2 = | t/2- 1 |
When t/2- 1 >: 0, t>2, S=t/2- 1.
When t=2, s = 0.
At t<2, S= 1-t/2.