(20 1 1 Shandong Yantai 26 14 minutes) As shown in the figure, in the rectangular coordinate system, the base AB of the trapezoidal ABCD is on the X axis, and the endpoint D of the base CD is.

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(1) Substitute Y = 4 into Y =-X+ to get X = 1.

The coordinate of point ∴ C is (1, 4).

When y = 0 and -x+= 0,

∴ X = 4。 The coordinate of point B is (4,0).

(2) If CM ⊥ AB is in m, then cm = 4 and BM = 3.

∴ BC = = 5.

∴sin∠ ABC = =。

① when 0 < t < 4, let QN ⊥ OB be n,

Then qn = bqsin ∠ ABC = t.

∴ S = OP QN = (4- t )× t =- t 2 + t (0< t