Vector Algebra
31 Board Maths previous year questions on Vector Algebra — options free on every question; 3 include the answer & explanation free, the rest unlock with PYQ Pass.
\(\text{ If }\vec{a}\text{ and }\vec{b}\text{ are two unit vectors, then }\vec{a}\cdot \vec{b}=...........\)
\(\cos \left(\theta \right)\)
|a|=1 , |b|=1 because they are the unit vectors.
\((\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})=\)
\(9\vec{i}-\vec{j}+3\vec{k}\)
The given vectors are \((\vec{i}+3\vec{j}-2\vec{k})\) and \((-\vec{i}+3\vec{k})\).
\((\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})\) represents the cross product of two vectors.
\((\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})=\left|\begin{matrix}\vec{i} & \vec{j} & \vec{k} \\ 1 & 3 & -2 \\ -1 & 0 & 3\end{matrix}\right|\\ (\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})=\vec{i}\left|\begin{matrix}3 & -2 \\ 0 & 3\end{matrix}\right|-\vec{j}\left|\begin{matrix}1 & -2 \\ -1 & 3\end{matrix}\right|+\vec{k}\left|\begin{matrix}1 & 3 \\ -1 & 0\end{matrix}\right|\\ (\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})=\vec{i}(9-0)-\vec{j}(3-2)+\vec{k}(0+3)\\ (\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})=9\vec{i}-\vec{j}+3\vec{k}\)
Hence, the value of \((\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})\) is \(9\vec{i}-\vec{j}+3\vec{k}.\)
Let \(\vec{p}\) and \(\vec{q}\) be two unit vectors and \(\alpha\) be the angle between them. Then \((\vec{p}+\vec{q})\) will be a unit vector for what value of \(\alpha\) ?
\(\frac{2\pi }{3}\)
Given, \(\left|\vec{p}+\vec{q}\right|=\left|\vec{p}\right|=\left|\vec{q}\right|=1\)
Now,
\({\left|\vec{p}+\vec{q}\right|}^{2}={\left|\vec{p}\right|}^{2}+{\left|\vec{q}\right|}^{2}+2\vec{p}\cdot \vec{q}\)
\(\Rightarrow {1}^{2}=1+1+2\cos \alpha\)
\(\Rightarrow 1=2+2\cos \alpha\)
\(\Rightarrow \cos \alpha =-\frac{1}{2}\)
\(\Rightarrow \alpha =\frac{2\pi }{3}\)
\(\text{ If }\vec{a}\text{ and }\vec{b}\text{ are two unit vectors, then }\vec{a}\cdot \vec{b}=...........\)
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Let \(\vec{a}=2\hat{i}−\hat{j}+\hat{k}\) and \(\vec{b}=\lambda \hat{j}+2\hat{k},\text{ }\lambda \in Z\) be the two vectors. Let \(\vec{c}=\vec{a}\times \vec{b}\) and \(\vec{d}\) be the vector of magnitude \(2\) in \(yz\)-plane. If \(\left|\vec{c}\right|=\sqrt{53},\) then the maximum possible value of \((\vec{c} \cdot \vec{d})^2\) is equal to:
[JEE Main 2026, 22 Jan (Shift 2)]
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\(\left|\vec{i}-\vec{j}-\vec{k}\right|=\)
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For any two vectors \(\vec{a}\) and \(\vec{b}\), which of the following statements is always true?
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For any two vectors \(\vec{a}\) and \(\vec{b}\), which of the following statements is always true?
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The projection vector of vector \(\vec{a}\) on vector \(\vec{b}\) is
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The vector with terminal point \(\mathrm{A}(2,-3,5)\) and initial point \(\mathrm{B}(3,-4,7)\) is :
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The unit vector perpendicular to both vectors \(\hat{i}+\hat{k}\) and \(\hat{i}-\hat{k}\) is:
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The projection vector of \(\vec{a}\) on \(\vec{b}\) is
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\(\vec{j}.\vec{j}=\)
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\((4\vec{i}+3\vec{j}+3\vec{k}).(6\vec{i}-4\vec{j}+\vec{k})=\)
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The position vectors of points P and Q are \(\vec{p}\) and \(\vec{q}\) respectively. The point R divides line segment PQ in the ratio 3: 1 and S is the mid-point of line segment PR. The position vector of S is :
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\((\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})=\)
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Let \(\theta\) be the angle between two unit vectors \(\hat{\mathrm{a}}\) and \(\hat{\mathrm{b}} \operatorname{such}\) that \(\sin \theta=\frac{3}{5}\). Then, \(\hat{a} \cdot \hat{b}\) is equal to :
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Let \(\theta\) be the angle between two unit vectors \(\hat{\mathrm{a}}\) and \(\hat{\mathrm{b}} \operatorname{such}\) that \(\sin \theta=\frac{3}{5}\). Then, \(\hat{a} \cdot \hat{b}\) is equal to :
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The unit vector perpendicular to both vectors \(\hat{i}+\hat{k}\) and \(\hat{i}-\hat{k}\) is:
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The vector with terminal point \(\mathrm{A}(2,-3,5)\) and initial point \(\mathrm{B}(3,-4,7)\) is :
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\((4\vec{i}+3\vec{j}+3\vec{k}).(6\vec{i}-4\vec{j}+\vec{k})=\)
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\(\vec{j}.\vec{j}=\)
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Let \(\vec{p}\) and \(\vec{q}\) be two unit vectors and \(\alpha\) be the angle between them. Then \((\vec{p}+\vec{q})\) will be a unit vector for what value of \(\alpha\) ?
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The position vectors of points \(P\) and \(Q\) are \(\vec{p}\) and \(\vec{q}\) respectively. The point \(R\) divides line segment \(PQ\) in the ratio \(3:1\) and \(S\) is the mid-point of line segment \(PR\). The position vector of \(S\) is :
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\(\left|\vec{i}-\vec{j}-\vec{k}\right|=\)
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If \(\vec{a}\) and \(\vec{b}\) are two non-zero vectors, then \(\vec{a}\cdot \vec{b}=-|\vec{a}||\vec{b}|\), if -
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\(1+{\cot }^{2}\theta =\)
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If the magnitude of two vectors \(\vec{a}\) and \(\vec{b}\) are \(\sqrt{3}\) and 2 respectively and \(\vec{a}\cdot \vec{b}=\sqrt{6}\), then the angle between \(\vec{a}\) and \(\vec{b}\) is -
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The value of \(\hat{i}\cdot (\hat{j}\times \hat{k})+\hat{j}\cdot (\hat{i}\times \hat{k})+\hat{k}\cdot (\hat{i}\times \hat{j})\) is -
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The value of \(\hat{i}\cdot (\hat{j}\times \hat{k})+\hat{j}\cdot (\hat{i}\times \hat{k})+\hat{k}\cdot (\hat{i}\times \hat{j})\) is:
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Direction : Two statements are given one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the following options :
Assertion (A) : The vectors
\(\vec{\mathrm{a}}=6\hat{\mathrm{i}}+2\hat{\mathrm{j}}-8\hat{\mathrm{k}}\\ \vec{\mathrm{b}}=10\hat{\mathrm{i}}-2\hat{\mathrm{j}}-6\hat{\mathrm{k}}\\ \vec{\mathrm{c}}=4\hat{\mathrm{i}}-4\hat{\mathrm{j}}+2\hat{\mathrm{k}}\)
represent the sides of a right angled triangle.
Reason (R) : Three non-zero vectors of which none of two are collinear forms a triangle if their resultant is zero vector or sum of any two vectors is equal to the third.
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