Math Problem Statement
if the sum of the first three terms in a geometric progression is 112 and the sum of the next three terms is 14. how many terms does it take for the sum to be greater than 125
Solution
We need to solve this step by step:
Step 1: Represent the first three terms in a geometric progression.
Let the first term be and the common ratio be . The first three terms are: The sum of these terms is given as: a + ar + ar^2 = 112 \tag{1}
Step 2: Represent the next three terms.
The next three terms are: The sum of these terms is given as: ar^3 + ar^4 + ar^5 = 14 \tag{2}
Step 3: Factorize both equations.
From equation (1):
From equation (2):
Step 4: Divide equation (2) by equation (1).
Step 5: Solve for using .
Substitute into equation (1):
Step 6: General formula for the sum of terms.
The sum of the first terms of a geometric progression is: Substitute and :
Step 7: Determine for .
Take the logarithm (base 2): Using : Since must be an integer, .
Final Answer:
It takes 6 terms for the sum to exceed 125.
Would you like a more detailed explanation or clarification on any step?
Here are some related questions to explore:
- How do logarithmic properties help solve exponential equations?
- What is the derivation of the sum formula for a geometric progression?
- How does the common ratio influence the growth or decay of a sequence?
- Can this result be verified using numerical methods or simulations?
- How does the choice of base for the logarithm affect the calculation?
Tip: Always verify calculations involving logarithms with precise values or a calculator for better accuracy!
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Math Problem Analysis
Mathematical Concepts
Geometric Progression
Logarithms
Sequences and Series
Formulas
Sum of the first n terms of a geometric progression: S_n = a(1 - r^n) / (1 - r) for |r| < 1
Logarithm property: log_b(a^n) = n * log_b(a)
Theorems
Properties of geometric progressions
Logarithmic rules for solving exponential equations
Suitable Grade Level
Grades 10-12