Write the solution set of the equation $x^{2} + x - 2 = 0$ in roster form.
A$\{1, 2\}$
B$\{1, -2\}$
C$\{-1, 2\}$
D$\{-1, -2\}$
Answer & Solution
Correct answer: B. $\{1, -2\}$
Factor: $x^{2} + x - 2 = (x - 1)(x + 2) = 0$.
Setting each factor to zero: $x - 1 = 0 \Rightarrow x = 1$, and $x + 2 = 0 \Rightarrow x = -2$.
Solution set in roster form: $\{1, -2\}$.
Check: $1^{2} + 1 - 2 = 0$ ✓ and $(-2)^{2} + (-2) - 2 = 4 - 2 - 2 = 0$ ✓.
- Trap A misses the negative root.
- Traps C, D have wrong signs.
NCERT Class 11, Example 1.
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