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Several problems in science and mathematics
1.b(2 HCl+Fe = FeCl 2+H2)(2 HCl+CaCO3 = H2O+CO2+CaCl 2)(HCl+NaOH = H2O+naclo)

2. A polygon with equal sides and angles is a regular polygon. Let the number of sides of one polygon be x and the number of sides of another polygon be 2x. The sum of the interior angles of a polygon is (n-2) x180 (x-2) x180/x divided by (2x-2) x180/2x = 3/4x = 52x = 65438.

3.(n-20)x 180 = 2570n = 130D

When 4N+N*(N-3)/2 is less than 20, the number divisible by 5 is 5, 15, 10, and n is d.