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Let $S$ be the set of distinct values of $b$ for which the linear system $x+y+z=1$, $x+ay+z=1$, $ax+by+z=0$ has no solution. Describe the set $S$.
Subtract equation 1 from equation 2: $(a-1)y = 0$.
Case $a\neq1$: $y=0$. Then from eq.1 and eq.3: $x+z=1$ and $ax+z=0$, giving $(a-1)x=-1$, so $x=\frac{-1}{a-1}$. This always has a solution for $a\neq1$.
Case $a=1$: System becomes $x+y+z=1$, $x+y+z=1$, $x+by+z=0$. The third equation forces $-1=by-... $ i.e. subtracting eq.1: $(b-1)y=-1$. For no solution we need $b=1$.
So $S=\{1\}$ β a single value. Hence $S$ is a singleton.
Students are typically classified as gifted when their IQ score is 130 or above by most modern definitions, but the traditional benchmark used in many Pakistani textbooks and exam papers is 140 and above for “genius/highly gifted.” In the context of this exam, the expected answer is C — 140 and above.
Correct Answer: C — 140 and above.
Which of the following is a solution to $x + x^2 = 1$?
Test each option in $x + x^2 = 1$:
- $x = -1$: $(-1) + (-1)^2 = -1 + 1 = 0 \neq 1$
- $x = 0$: $0 + 0 = 0 \neq 1$
- $x = \dfrac{1}{2}$: $\dfrac{1}{2} + \dfrac{1}{4} = \dfrac{3}{4} \neq 1$
- $x = 1$: $1 + 1 = 2 \neq 1$
Solving $x^2 + x - 1 = 0$: $x = \dfrac{-1 \pm \sqrt{5}}{2}$, which gives irrational values not among the standard choices. Therefore, none of the listed options is a solution.
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