Q. Find the 13th term of the geometric sequence 3,−12,48,…Answer:
Identify type and first term: Identify the type of sequence and the first term (a1).The sequence 3,−12,48,extellipsis is a geometric sequence because each term is multiplied by a common ratio to get the next term. The first term is a1=3.
Find common ratio: Find the common ratio r of the sequence.To find the common ratio, divide the second term by the first term: r=(−12)/3=−4.
Use nth term formula: Use the formula for the nth term of a geometric sequence.The formula for the nth term an of a geometric sequence is an=a1⋅r(n−1).
Substitute values for 13th term: Substitute the values of a1 and r into the formula to find the 13th term.a13=3×(−4)13−1=3×(−4)12.
Calculate 13th term: Calculate the 13th term.Since (−4)12 is a positive number because 12 is an even exponent, we have a13=3×(412).