quiz
Mathematics EN 9th gradeBet on your knowledge, not on luck

What are rational numbers?
They are numbers that can be written in fraction form:
\( \frac{a}{b}, \quad b \neq 0 \)
Examples:
\( \frac{3}{4}, -2, 0{,}5, -\frac{7}{3} \)
valor absoluto
The valor absoluto represents the distance to zero:
\( |a| = a \) se \( a \geq 0 \)
\( |a| = -a \) se \( a < 0 \)
Examples:
\( |5| = 5 \)
\( |-5| = 5 \)
Simétrico
The Simétrico of a number is:
\( -a \)
Examples:
\( 3 \rightarrow -3 \)
\( -7 \rightarrow 7 \)
Adição e subtração
Addition with the same sign
Add the values and keep the sign
Examples:
\( 3 + 5 = 8 \)
\( -4 + (-6) = -10 \)
Soma com sinais contrários
Subtract the values and take the sign of the number with the greatest absolute valueNL# Examples:
\( 7 + (-3) = 4 \)
\( -8 + 5 = -3 \)
Soma de números simétricos
The result is always zero
\( a + (-a) = 0 \)
Examples:
\( 5 + (-5) = 0 \)
Subtração (diferença)
It is transformed into the sum of the opposite
\( a - b = a + (-b) \)
Examples:
\( 7 - 3 = 7 + (-3) = 4 \)
\( 5 - (-2) = 5 + 2 = 7 \)
Divisão de números racionais
Main rule
Multiply by the reciprocal
\( \frac{a}{b} \div \frac{c}{d} = \frac{a}{b} \times \frac{d}{c} \) Inverso de um número racional
Swap the numerator and denominator
\( \text{Inverso de } \frac{a}{b} = \frac{b}{a}, \quad a \neq 0 \)
Examples:
\( \frac{3}{4} \rightarrow \frac{4}{3} \)
\( 2 = \frac{2}{1} \rightarrow \frac{1}{2} \)
Important:
\( 0 \text{ não tem inverso} \)
Examples de divisão
\( \frac{2}{3} \div \frac{4}{5} = \frac{2}{3} \times \frac{5}{4} = \frac{10}{12} = \frac{5}{6} \)
TIPS
✔ Same signs → add and keep the sign ✔ Different signs → subtract and take the sign of the number with the greatest absolute value ✔ Subtraction → convert to addition ✔ Division → multiply by the reciprocal ✔ Número + simétrico: \( a + (-a) = 0 \)
✔ Valor absoluto: \( |a| \geq 0 \)