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  1. Home
  2. 12th grade
  3. Precalculus
  4. Exercise : Solve equations involving greatest integer function with calculations

Solve equations involving greatest integer function with calculations Precalculus

Solve the following equations.

\lfloor x-\dfrac{2}{3} \rfloor=4

\lfloor E\left(x\right) \rfloor=a if and only if a\leqslant E\left(x\right)\lt a+1.

Therefore:

\lfloor x-\dfrac{2}{3} \rfloor=4

If and only if:

4\leqslant x-\dfrac{2}{3}\lt5

Adding \dfrac{2}{3} to all sides gives:

4+\dfrac{2}{3} \leqslant x\lt5+\dfrac{2}{3}

\dfrac{14}{3}\leqslant x\lt\dfrac{17}{3}

x is a solution if and only if \dfrac{14}{3}\leqslant x\lt\dfrac{17}{3}.

\lfloor 2x+\dfrac{5}{6} \rfloor=3

\lfloor E\left(x\right) \rfloor=a if and only if a\leqslant E\left(x\right)\lt a+1.

Therefore:

\lfloor 2x+\dfrac{5}{6} \rfloor=3

If and only if:

3\leqslant 2x+\dfrac{5}{6}\lt4

Subtracting \dfrac{5}{6} from all sides gives:

3-\dfrac{5}{6} \leqslant 2x\lt4-\dfrac{5}{6}

\dfrac{13}{6}\leqslant 2x\lt\dfrac{19}{6}

Dividing all sides by 2 gives:

\dfrac{13}{12}\leqslant x\lt\dfrac{19}{12}

x is a solution if and only if \dfrac{13}{12}\leqslant x\lt\dfrac{19}{12}.

\lfloor 4x-\dfrac{1}{2} \rfloor=7

\lfloor E\left(x\right) \rfloor=a if and only if a\leqslant E\left(x\right)\lt a+1.

Therefore:

\lfloor 4x-\dfrac{1}{2} \rfloor=7

If and only if:

7\leqslant 4x-\dfrac{1}{2}\lt8

Adding \dfrac{1}{2} to all sides gives:

7+\dfrac{1}{2} \leqslant 4x\lt8+\dfrac{1}{2}

\dfrac{15}{2}\leqslant 4x\lt\dfrac{17}{2}

Dividing all sides by 4 gives:

\dfrac{15}{8}\leqslant x\lt\dfrac{17}{8}

x is a solution if and only if \dfrac{15}{8}\leqslant x\lt\dfrac{17}{8}.

\lfloor 3x-5 \rfloor=1

\lfloor E\left(x\right) \rfloor=a if and only if a\leqslant E\left(x\right)\lt a+1.

Therefore:

\lfloor 3x-5 \rfloor=1

If and only if:

1\leqslant 3x-5\lt2

Adding 5 to all sides gives:

6 \leqslant 3x\lt7

Dividing all sides by 3 gives:

2\leqslant x\lt\dfrac{7}{3}

x is a solution if and only if 2\leqslant x\lt\dfrac{7}{3}.

\lfloor \dfrac{1}{3}x+\dfrac{5}{6} \rfloor=2

\lfloor E\left(x\right) \rfloor=a if and only if a\leqslant E\left(x\right)\lt a+1.

Therefore:

\lfloor \dfrac{1}{3}x+\dfrac{5}{6} \rfloor=2

If and only if:

2\leqslant \dfrac{1}{3}x+\dfrac{5}{6}\lt3

Subtracting \dfrac{5}{6} from all sides gives:

2-\dfrac{5}{6} \leqslant \dfrac{1}{3}x\lt3-\dfrac{5}{6}

\dfrac{7}{6} \leqslant \dfrac{1}{3}x\lt\dfrac{13}{6}

Multiplying all sides by 3 gives:

\dfrac{7}{2}\leqslant x\lt\dfrac{13}{2}

x is a solution if and only if \dfrac{7}{2}\leqslant x\lt\dfrac{13}{2}.

\lfloor \dfrac{2}{5}x-\dfrac{7}{6} \rfloor=5

\lfloor E\left(x\right) \rfloor=a if and only if a\leqslant E\left(x\right)\lt a+1.

Therefore:

\lfloor \dfrac{2}{5}x-\dfrac{7}{6} \rfloor=5

If and only if:

5\leqslant \dfrac{2}{5}x-\dfrac{7}{6}\lt6

Adding \dfrac{7}{6} to all sides gives:

5+\dfrac{7}{6} \leqslant \dfrac{2}{5}x\lt6+\dfrac{7}{6}

\dfrac{37}{6} \leqslant \dfrac{2}{5}x\lt\dfrac{43}{6}

Multiplying all sides by \dfrac{5}{2} gives:

\dfrac{185}{12}\leqslant x\lt\dfrac{215}{12}

x is a solution if and only if \dfrac{185}{12}\leqslant x\lt\dfrac{215}{12}.

\lfloor 3x+\dfrac{1}{7} \rfloor=0

\lfloor E\left(x\right) \rfloor=a if and only if a\leqslant E\left(x\right)\lt a+1.

Therefore:

\lfloor 3x+\dfrac{1}{7} \rfloor=0

If and only if:

0\leqslant 3x+\dfrac{1}{7}\lt1

Subtracting \dfrac{1}{7} from all sides gives:

0-\dfrac{1}{7} \leqslant 3x\lt1-\dfrac{1}{7}

-\dfrac{1}{7} \leqslant 3x\lt\dfrac{6}{7}

Dividing all sides by 3 gives:

-\dfrac{1}{21}\leqslant x\lt\dfrac{2}{7}

x is a solution if and only if -\dfrac{1}{21}\leqslant x\lt\dfrac{2}{7}.

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See also
  • Course : Greatest integer function
  • Exercise : Calculate expressions involving greatest integer functions
  • Exercise : Solve inequalities involving greatest integer function with calculations
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