Math Problem Statement

Find all x in the range 0 to 29 such that: x^2 = x (mod 30)

Solution

To solve for all values of xx in the range 0x290 \leq x \leq 29 such that:

x2x(mod30)x^2 \equiv x \pmod{30}

we start by rearranging the equation:

x2x0(mod30)x^2 - x \equiv 0 \pmod{30}

This can be factored as:

x(x1)0(mod30)x(x - 1) \equiv 0 \pmod{30}

Thus, x(x1)x(x - 1) must be divisible by 30. Since 30=23530 = 2 \cdot 3 \cdot 5, x(x1)x(x - 1) must be divisible by 2, 3, and 5.

Step 1: Analyzing x(x1)x(x - 1) for Divisibility by 2, 3, and 5

Since xx and x1x - 1 are consecutive integers, one of them is always even, so x(x1)x(x - 1) is divisible by 2.

Similarly, one of xx or x1x - 1 must be divisible by 3.

Finally, for x(x1)x(x - 1) to be divisible by 5, either xx or x1x - 1 must be divisible by 5.

Step 2: Possible Solutions

The divisibility requirements imply that xx must satisfy the following conditions:

  1. xx or x1x - 1 must be divisible by 2, 3, and 5.
  2. This occurs when x0(mod30)x \equiv 0 \pmod{30} or x1(mod30)x \equiv 1 \pmod{30}.

Step 3: Valid Solutions in the Given Range

Since we only need solutions for 0x290 \leq x \leq 29, we check:

  1. x=0x = 0
  2. x=1x = 1

Verification

  1. For x=0x = 0: x2=00(mod30)x^2 = 0 \equiv 0 \pmod{30}

  2. For x=1x = 1: x2=11(mod30)x^2 = 1 \equiv 1 \pmod{30}

Both values satisfy the condition x2x(mod30)x^2 \equiv x \pmod{30}.

Conclusion

The solutions are: x=0 and x=1x = 0 \text{ and } x = 1

Would you like a deeper explanation of any part of this solution?

Here are five related questions to further explore modular arithmetic and divisibility:

  1. How would you solve for xx in x3=x(mod30)x^3 = x \pmod{30}?
  2. Can you determine all values of xx such that x2=x(modn)x^2 = x \pmod{n} for different values of nn?
  3. What are other interesting properties of solutions to equations of the form xk=x(modn)x^k = x \pmod{n}?
  4. How can we use the Chinese Remainder Theorem to solve similar modular equations?
  5. What happens to the solutions if we expand the range to x<60x < 60?

Tip: Modular equations often simplify by factoring and analyzing each factor's divisibility conditions.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Modular Arithmetic
Divisibility
Congruences

Formulas

x^2 ≡ x (mod n) implies x(x - 1) ≡ 0 (mod n)

Theorems

Divisibility Rules
Chinese Remainder Theorem (implicitly relevant)

Suitable Grade Level

Grades 10-12