Modgifrac Equation

Algebra Level 4

2 x 1 = 3 x + 2 { x } \large |2x-1|=3 \lfloor x\rfloor+2\{x\}

How many values of x x satisfy the equation above?

Notations:

7 3 2 4 5 0 6 1

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1 solution

Zee Ell
Nov 5, 2016

2 x 1 = 3 x + 2 { x } |2x - 1| = 3 \lfloor {x} \rfloor + 2 \{ x \}

Since:

x = x + { x } x = \lfloor {x} \rfloor + \{ x \}

Therefore:

2 x 1 = 3 x + 2 { x } 2 x 1 = 2 x + x |2x - 1| = 3 \lfloor {x} \rfloor + 2 \{ x \} \iff |2x - 1| = 2x + \lfloor x \rfloor

Now, we have two cases:

1.) 2 x 1 0 x 0.5 2x -1 ≥ 0 \iff x ≥ 0.5

2 x 1 = 2 x + x 2x - 1 = 2x + \lfloor x \rfloor

1 = x - 1 = \lfloor x \rfloor

1 x < 0 -1 ≤ x < 0

However, since x ≥ 0.5 we don't have any solutions in this case.

2.) 2 x 1 < 0 x < 0.5 2x -1 < 0 \iff x < 0.5

1 2 x = 2 x + x 1- 2x = 2x + \lfloor x \rfloor

1 = 4 x + x 1 = 4x + \lfloor x \rfloor

If x is negative, then it's floor is also negative, so we would have a negative number on the RHS, which cannot be equal the positive LHS, so no solution here.

If 0 ≤ x < 0.5 , then:

x = 0 \lfloor x \rfloor = 0

Therefore:

1 = 4x

x = 0.25

This means, that we only have one solution (x = 0.25).

Hence, our answer should be: 1 \text {Hence, our answer should be: } \boxed {1}

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