Math Problem Statement

Evaluate the sum \( \sum_{i=1}^{28} (i - 1)^2 \). Use the properties of summation and the Summation Formulas Theorem to find the result.

Solution

The given sum is:

i=128(i1)2\sum_{i=1}^{28} (i - 1)^2

To evaluate this summation, let's break it down.

  1. The expression inside the summation is (i1)2(i - 1)^2, which we need to sum from i=1i = 1 to i=28i = 28.

  2. To simplify, notice that when i=1i = 1, (i1)2=02=0(i - 1)^2 = 0^2 = 0, and for other values of ii, we sum the squares of integers up to 2727 (since i1i-1 ranges from 0 to 27).

So, this sum becomes:

i=128(i1)2=i=027i2\sum_{i=1}^{28} (i - 1)^2 = \sum_{i=0}^{27} i^2

This is a standard sum of squares, and the formula for the sum of squares of the first nn integers is:

i=1ni2=n(n+1)(2n+1)6\sum_{i=1}^{n} i^2 = \frac{n(n+1)(2n+1)}{6}

In this case, n=27n = 27. Plugging this into the formula:

i=127i2=27(27+1)(2×27+1)6=27(28)(55)6\sum_{i=1}^{27} i^2 = \frac{27(27+1)(2 \times 27 + 1)}{6} = \frac{27(28)(55)}{6}

Now, simplify:

27×28×556=6930\frac{27 \times 28 \times 55}{6} = 6930

Thus, the value of the sum is:

i=128(i1)2=6930\sum_{i=1}^{28} (i - 1)^2 = 6930

Would you like further clarification on any of the steps?

Here are some follow-up questions you might explore:

  1. What is the general formula for summing cubes of integers?
  2. How would the sum change if we summed (i1)3(i-1)^3 instead of (i1)2(i-1)^2?
  3. Can you derive the formula for the sum of squares of integers from scratch?
  4. How does this method extend to summing powers higher than squares?
  5. What happens if you change the upper bound (28) to another number?

Tip: Always double-check your final summation using graphing or summation tools to verify complex calculations!

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Math Problem Analysis

Mathematical Concepts

Summation
Algebra
Sequences and Series

Formulas

Sum of squares: \( \sum_{i=1}^{n} i^2 = \frac{n(n+1)(2n+1)}{6} \)

Theorems

Summation Formulas Theorem

Suitable Grade Level

High School (Grades 10-12)