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 As shown in the figure, overlap the right-angle vertices of the two triangular boards.
(1) Write the equal angles with vertex C;
(2) If ∠ACB = 150°, calculate the measure of ∠DCE;
(3) Describe the quantitative relationship between ∠ACB and ∠DCE;
(4) When the triangular board ACD is rotated about point C, does the relationship you described in (3) change? Please explain your reasoning.