Math Problem Statement

(a) Find the sum of all the terms of the geometric sequence 1, 2, 4, ••., 64. (b) Let a be a constant, where a > 0. (i) Simplify a x a^2x a^4 x ... x a ^65 (i) Simplify log a + log a ^2+ log a ^4+ ... + log a ^64

Solution

(a) Find the sum of all the terms of the geometric sequence 1,2,4,,641, 2, 4, \dots, 64:

This is a geometric sequence where the first term a1=1a_1 = 1 and the common ratio r=2r = 2. The last term is 6464, so we need to find the sum of the sequence.

The formula for the sum of the first nn terms of a geometric sequence is:

Sn=a1(1rn)1rS_n = \frac{a_1 (1 - r^n)}{1 - r}

To determine nn, we use the formula for the nn-th term of a geometric sequence:

an=a1rn1a_n = a_1 r^{n-1}

Given an=64a_n = 64, we solve for nn:

64=12n164 = 1 \cdot 2^{n-1} 64=2n164 = 2^{n-1} n1=6n=7n-1 = 6 \quad \Rightarrow \quad n = 7

Now we can find the sum:

S7=1(127)12=1(1128)1=1271=127S_7 = \frac{1 (1 - 2^7)}{1 - 2} = \frac{1 (1 - 128)}{-1} = \frac{-127}{-1} = 127

Thus, the sum of all the terms of the geometric sequence is:

127\boxed{127}


(b) (i) Simplify a×a2×a4××a64a \times a^2 \times a^4 \times \dots \times a^{64}:

This is a product of powers of aa. To simplify, we add the exponents:

a×a2×a4××a64=a1+2+4++64a \times a^2 \times a^4 \times \dots \times a^{64} = a^{1 + 2 + 4 + \dots + 64}

This is a sum of powers of 2: 1+2+4+8+16+32+641 + 2 + 4 + 8 + 16 + 32 + 64.

This sum is a geometric series with a1=1a_1 = 1, r=2r = 2, and the number of terms n=7n = 7. The sum of the exponents is:

S=1(271)21=271=1281=127S = \frac{1(2^7 - 1)}{2 - 1} = 2^7 - 1 = 128 - 1 = 127

Thus, the simplified expression is:

a127a^{127}


(b) (ii) Simplify loga+loga2+loga4++loga64\log a + \log a^2 + \log a^4 + \dots + \log a^{64}:

Using the logarithm property log(xy)=ylog(x)\log(x^y) = y \log(x), we can rewrite each term:

loga1+loga2+loga4++loga64=1loga+2loga+4loga++64loga\log a^1 + \log a^2 + \log a^4 + \dots + \log a^{64} = 1 \log a + 2 \log a + 4 \log a + \dots + 64 \log a

Factor out loga\log a:

loga(1+2+4++64)\log a (1 + 2 + 4 + \dots + 64)

We already calculated the sum 1+2+4++64=1271 + 2 + 4 + \dots + 64 = 127, so:

127loga127 \log a

Thus, the simplified expression is:

127loga\boxed{127 \log a}


Would you like further details on any part of the solution? Here are some related questions for more exploration:

  1. How do you find the sum of the first nn terms of an arithmetic series?
  2. What is the general formula for the sum of an infinite geometric series?
  3. How would the sum change if the common ratio was less than 1?
  4. How can you express the product of terms in a geometric progression using logarithms?
  5. Can you explain how logarithmic identities simplify complex expressions?

Tip: Always remember that geometric sequences grow exponentially, and logarithms help simplify exponential expressions.

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Math Problem Analysis

Mathematical Concepts

Geometric Sequences
Exponents
Logarithms
Geometric Series

Formulas

Sum of geometric sequence: S_n = a_1 * (1 - r^n) / (1 - r)
Exponent product rule: a^m * a^n = a^(m+n)
Logarithm properties: log(x^y) = y * log(x)

Theorems

Properties of Geometric Progressions
Exponent Rules
Logarithmic Identities

Suitable Grade Level

Grades 10-12