Q. Find the sum of the first 9 terms of the following series, to the nearest integer.54,36,24,…Answer:
Identify pattern: Identify the pattern in the series.The series is 54,36,24,… which seems to be a geometric series because each term is multiplied by a common ratio to get the next term. To find the common ratio (r), we divide the second term by the first term.r=5436
Calculate common ratio: Calculate the common ratio.r=5436=32The common ratio is 32.
Use formula for sum: Use the formula for the sum of the first n terms of a geometric series.The formula for the sum of the first n terms (Sn) of a geometric series is:Sn=a×(1−rn)/(1−r), where a is the first term and r is the common ratio.For this series, a=54, r=2/3, and n=9.
Substitute values and calculate: Substitute the values into the formula and calculate the sum.S9=54×(1−(32)9)/(1−32)
Evaluate expression: Evaluate the expression.S9=54×(1−(32)9)/(31)First, calculate (32)9.(32)9=(3929)
Calculate powers: Calculate (29) and (39).29=51239=19683Now, substitute these values back into the expression.
Continue calculation: Continue the calculation.S9=54×(1−19683512)/(31)S9=54×(1968319683−19683512)/(31)S9=54×(1968319171)/(31)
Simplify expression: Simplify the expression.S9=54×(19171/19683)×3S9=54×3×(19171/19683)S9=162×(19171/19683)
Perform division: Perform the division.S9=162×(19171/19683)S9≈162×0.974
Multiply for sum: Multiply to find the sum.S9≈162×0.974S9≈157.788
Round to nearest integer: Round to the nearest integer. S9≈158