CBSE 2026 · Region 1 · Set 1 · Q20 · 1 mark
Assertion (A) : Lines given by $\displaystyle x=\mathrm{py}+\mathrm{q}, \mathrm{z}=\mathrm{ry}+\mathrm{s}$ and $\displaystyle x=\mathrm{p}^{\prime} \mathrm{y}+\mathrm{q}^{\prime}$, $\displaystyle \mathrm{z}=\mathrm{r}^{\prime} \mathrm{y}+\mathrm{s}^{\prime}$ are perpendicular to each other when $\displaystyle \mathrm{pp}^{\prime}+\mathrm{rr}^{\prime}=1$.
Reason (R) : Two lines $\displaystyle \vec{\mathrm{r}}=\vec{a}_{1}+\lambda \vec{b}_{1}$ and $\displaystyle \vec{\mathrm{r}}=\vec{a}_{2}+\mu \vec{b}_{2}$ are perpendicular to each other if $\displaystyle \vec{b}_{1} \cdot \vec{b}_{2}=0$.
Official answer
From CBSE’s own marking scheme for this paper.
(D)
Assertion (A) is false and Reason (R) is true.
Three Dimensional GeometryAngle between Two LinesAnalyseassertion_reasonmedium
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CBSE Class 12 Mathematics past-paper question from the 2026board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.