For the sequence, \( -2,2,6,10, \ldots \), calculate \( n \) if \( t_{n}=54 \).
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To find \( n \) such that \( t_n = 54 \) for the sequence \( -2, 2, 6, 10, \ldots \), we first need to determine the formula for the \( n \)-th term of the sequence. By examining the sequence, the common differences between terms are: - \( 2 - (-2) = 4 \) - \( 6 - 2 = 4 \) - \( 10 - 6 = 4 \) The sequence is an arithmetic sequence with a first term \( a = -2 \) and a common difference \( d = 4 \). The formula for the \( n \)-th term of an arithmetic sequence can be written as: \[ t_n = a + (n-1)d \] Substituting in the values we have: \[ t_n = -2 + (n-1) \cdot 4 \] Simplifying this, we get: \[ t_n = -2 + 4n - 4 = 4n - 6 \] Now we set this equal to 54 to find \( n \): \[ 4n - 6 = 54 \] Adding 6 to both sides gives: \[ 4n = 60 \] Dividing both sides by 4, we find: \[ n = 15 \] Therefore, \( n \) is \( \boxed{15} \).