Taxicab Numbers and Cube Calculations

MathematicsNumber TheoryMedium

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3. Taxicab Numbers Exploration: (a) Verify that $1729 = 1^3 + 12^3 = 9^3 + 10^3$. (b) Express $4104$ as sum of two cubes in different ways. (c) Find if $1000$ can be expressed as sum of two positive cubes. 4. Calculate the following cubes: (a) $(2.5)^3$ (b) $(3/4)^3$ (c) $(-7)^3$

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1
Step 1

Let's dive into the fascinating world of Taxicab numbers and cube calculations. We will work through problem three regarding sums of cubes and problem four involving basic cube evaluations.

Taxicab Numbers & Cubes Exploration

2
Step 2

Starting with problem 3 a, we need to verify the famous Hardy Ramanujan number, one thousand seven hundred and twenty nine, is the sum of two different pairs of cubes.

3 (a) Verification

$$1^3 + 12^3 = 1 + 1728 = 1729$$
$$9^3 + 10^3 = 729 + 1000 = 1729$$
3
Step 3

Both calculations give one thousand seven hundred and twenty nine, so the verification is complete.

4
Step 4

Now for problem 3 b, let's express four thousand one hundred and four as the sum of two cubes in two different ways. Let's list some cubes near this value.

3 (b) Express 4104 as Sum of Two Cubes

nn^3
11
28
9729
101000
153375
164096
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Step 5

Notice that four thousand ninety six is very close to four thousand one hundred and four. The difference is eight, which is two cubed.

$$4104 = 4096 + 8 = 16^3 + 2^3$$
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Step 6

Next, let's try the cube of fifteen, which is three thousand three hundred seventy five. The difference is seven hundred twenty nine, which is exactly nine cubed.

$$4104 = 3375 + 729 = 15^3 + 9^3$$
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Step 7

In part c, we check if one thousand can be expressed as a sum of two positive cubes. We already know one thousand is ten cubed.

3 (c) 1000 as sum of cubes?

$$1000 = 10^3$$

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About This Question

Subject
Mathematics
Topic
Number Theory
Difficulty
Medium
Question Type
Open Ended

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