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

Solve inequalities involving greatest integer function with calculations Precalculus

Solve the following inequalities.

\lfloor x+\dfrac{4}{5} \rfloor \lt \dfrac{11}4

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

Therefore:

\lfloor x+\dfrac{4}{5} \rfloor \lt \dfrac{11}4

If and only if:

x+\dfrac{4}{5} \lt 3

Subtracting \dfrac{4}{5} from both sides gives:

x \lt 3-\dfrac{4}{5}

x \lt \dfrac{11}{5}

x is a solution if and only if x \lt \dfrac{11}{5}.

\lfloor 2x+\dfrac{1}{4} \rfloor \lt \dfrac{3}7

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

Therefore:

\lfloor 2x+\dfrac{1}{4} \rfloor\lt \dfrac{3}7

If and only if:

2x+\dfrac{1}{4} \lt 1

Subtracting \dfrac{1}{4} from both sides gives:

2x \lt 1-\dfrac{1}{4}

2x \lt \dfrac{3}{4}

Dividing both sides by 2 gives:

x \lt \dfrac{3}{8}

x is a solution if and only if x \lt \dfrac{3}{8}.

\lfloor \dfrac{1}{4}x-\dfrac{2}{3} \rfloor \lt \dfrac{7}3

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

Therefore:

\lfloor \dfrac{1}{4}x-\dfrac{2}{3} \rfloor \lt \dfrac{7}3

If and only if:

\dfrac{1}{4}x-\dfrac{2}{3} \lt 3

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

\dfrac{1}{4}x \lt 3+\dfrac{2}{3}

\dfrac{1}{4}x \lt \dfrac{11}{3}

Multiplying both sides by 4 gives:

x \lt \dfrac{44}{3}

x is a solution if and only if x \lt \dfrac{44}{3}.

\lfloor \dfrac{3}{4}x-\dfrac{1}{5} \rfloor \lt -\dfrac{13}6

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

Therefore:

\lfloor \dfrac{3}{4}x-\dfrac{1}{5} \rfloor \lt -\dfrac{13}6

If and only if:

\dfrac{3}{4}x-\dfrac{1}{5} \lt -2

Adding \dfrac{1}{5} to both sides gives:

\dfrac{3}{4}x \lt -2+\dfrac{1}{5}

\dfrac{3}{4}x \lt -\dfrac{9}{5}

Multiplying both sides by \dfrac{4}{3} :

x \lt -\dfrac{12}{5}

x is a solution if and only if x \lt -\dfrac{12}{5}.

\lfloor x-\dfrac{2}{3} \rfloor \gt \dfrac{5}6

\lfloor E\left(x\right) \rfloor\gt a if and only if E\left(x\right)\geq \lfloor a \rfloor+1.

Therefore:

\lfloor x-\dfrac{2}{3} \rfloor \gt \dfrac{5}6

If and only if:

x-\dfrac{2}{3} \geqslant1

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

x \geqslant 1+\dfrac{2}{3}

x \geqslant \dfrac{5}{3}

x is a solution if and only if x \geqslant \dfrac{5}{3}.

\lfloor 3x-\dfrac{1}{5} \rfloor\gt \dfrac{9}2

\lfloor E\left(x\right) \rfloor\gt a if and only if E\left(x\right)\geq \lfloor a \rfloor+1.

Therefore:

\lfloor 3x-\dfrac{1}{5} \rfloor \gt \dfrac{9}2

If and only if:

3x-\dfrac{1}{5} \geqslant5

Adding \dfrac{1}{5} to both sides gives:

3x \geqslant 5+\dfrac{1}{5}

3x \geqslant \dfrac{26}{5}

Dividing both sides by 3 gives:

x \geqslant \dfrac{26}{15}

x is a solution if and only if x \geqslant \dfrac{26}{15}.

\lfloor x+4 \rfloor\gt 2

\lfloor E\left(x\right) \rfloor\gt a if and only if E\left(x\right)\geq \lfloor a \rfloor+1.

Therefore:

\lfloor x+4 \rfloor\gt 2

If and only if:

x+4 \geqslant3

Subtracting 4 from both sides gives:

x\geqslant-1

x is a solution if and only if x\geqslant-1.

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