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If we remember that the order of the letters in the triangle name tell us which parts of each triangle are congruent, then we can see that <A is congruent to <D because they are in the same order in the letters in the name of the triangle. ( ^ABC = ^ DEC. A and D are in the same spot in the order of letters). So, if <A = 40 degrees, the m<D is 40 degrees.

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