If \(a_n=5\cdot3^{n-1}-2\), what will be \(a_4\)?
Answer and explanation
Correct answer: 133
Substituting \(n=4\) into the formula gives \(a_4=5\cdot3^{4-1}-2=5\cdot3^3-2=5\cdot27-2=133\). Therefore, 133 is correct. A value such as 131 can result from an error in evaluating \(3^3\) or in the subsequent multiplication. Exam tip: in expressions with exponents, simplify the exponent first, then evaluate the power and multiplication.
Frequently asked questions
What is the correct answer to this question?
133
Why is this the correct answer?
Substituting \(n=4\) into the formula gives \(a_4=5\cdot3^{4-1}-2=5\cdot3^3-2=5\cdot27-2=133\). Therefore, 133 is correct. A value such as 131 can result from an error in evaluating \(3^3\) or in the subsequent multiplication. Exam tip: in expressions with exponents, simplify the exponent first, then evaluate the power and multiplication.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: nth term.
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