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As shown in the figure, in the quadrilateral ABCD, ad ∥ BC, ∠ B = 90 °, ad = 16cm, ab = 4cm, BC = 21cm, the moving point P starts from point B and moves to point C at the speed of 2cm / s along the direction of line BC, the moving point Q starts from point a and moves to point d at the speed of 1cm / s along the direction of line ad, and points P and Q start from point B and a respectively. When point P moves to point C, point Q stops moving, and the time of motion is set (1) find the length of DQ (expressed by the algebraic expression of T); (2) when the value of T is, the area of △ PQD is equal to 12cm2? (3) Is there a point P such that △ PQD is a right triangle? If it exists, request all the values of t that meet the requirements; if not, explain the reason
(1) AQ = t × 1 = t, ∧ DQ = ad-aq = 16-t; (2) PE ⊥ ad at e, ∧ ad ∥ BC, B = 90 °, PE = AB = 4, ∧ s △ PQD = 12dq · PE = 12 (cm2), ∧ 12 × (16-t) × 4 = 12, the solution is t = 10, a: when t = 10 seconds, the area of △ PQD is equal to 12cm2; (3
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