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[tex]2.) \:a.) \\ Un = a + (n- 1) b \\ U12 = 4 + (12 - 1) - 2 \\ U12 = 4 + 11 \times - 2 \\ U12 = 4 + ( - 22) \\ U12 = 4 - 22 \\ U12 = - 18 \\ \\ 2.)\:b.) \\ Un = a + (n- 1) b \\ U8 = - 10 + (8 - 1) - 4 \\ U8 = - 10 + 7 \times - 4 \\ U8 = - 10 + ( - 28) \\ U8 = - 10 - 28 \\ U8 = - 38 \\ \\ 3.)\:a.) \\ Un = a + (n- 1) b \\ U6 = 5 + (6 - 1)b \\ 35 = 5 + 5 b \\ 5b = 35 - 5 \\ 5b = 30 \\ b = \frac{30}{5} \\ b = 6 \\ \\3.)\:b.) \\ Un = a + (n- 1) b \\ U5 = - 15 + (5 - 1)b \\ 25 = - 15 + 4b \\ 4b = 25 + 15 \\ 4b = 40 \\ b = \frac{40}{4} \\ b = 10[/tex]