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 Number sequences Write variable expressions for arithmetic sequences Write an expression to describe the sequence -3, -6, -9, -12,... Use n to represent the position of a term in the sequence, where n=1 for the first term. The sequence -3, -6, -9, -12,... looks like 1, 2, 3, 4,... except each term is multiplied by -3. So, the formula is -3n, where n represents the position of a term in the sequence. Check the first four terms: To find the 1st term, plug in n=1. -3n=-3(1)=-3 To find the 2nd term, plug in n=2. -3n=-3(2)=-6 To find the 3rd term, plug in n=3. -3n=-3(3)=-9 To find the 4th term, plug in n=4. -3n=-3(4)=-12 The sequence -3, -6, -9, -12,... is described by the expression -3n Write an expression to describe the sequence -7, -6, -5, -4,... Use n to represent the position of a term in the sequence, where n=1 for the first term. The sequence -7, -6, -5, -4,... looks like 1, 2, 3, 4,... except each term is 8 smaller. So, the formula is n-8, where n represents the position of a term in the sequence. Check the first four terms: To find the 1st term, plug in n=1. n-8=1-8=-7 To find the 2nd term, plug in n=2. n-8=2-8=-6 To find the 3rd term, plug in n=3. n-8=3-8=-5 To find the 4th term, plug in n=4. n-8=4-8=-4 The sequence -7, -6, -5, -4,... is described by the expression n-8.