Browse by Stream
QnA
Home
QnA
Go To Your Study Dashboard

Get Answers to all your Questions

header-bg qa
  • Home
  • School
  • Need Solution for R.D.Sharma Maths Class 12 Chapter 23 Scalar or Dot Products Exercise 23.1 Question 21 Maths Textbook Solution.

Need Solution for R.D.Sharma Maths Class 12 Chapter 23 Scalar or Dot  Products  Exercise 23.1 Question 21 Maths Textbook Solution.

Answers (1)

Answer:  < A=\frac{\pi }{4},< B=\frac{\pi }{2},< C=\frac{\pi }{4}

Hint: You must know the rules of finding angle of triangle

Given: Find angle of triangle A\left ( 0,-1,-2 \right ),B\left ( 3,1,4 \right ) and C\left ( 5,7,1 \right )

Solution: Given that,

                             \overrightarrow{O A}=0 \vec{\imath}-1 \hat{\jmath}-2 \hat{k}, \overrightarrow{O B}=3 \vec{\imath}+1 \hat{\jmath}+4 \hat{k}, \overrightarrow{O C}=5 \vec{\imath}+7 \hat{\jmath}+1 \hat{k}

\begin{aligned} &\overrightarrow{A B}=\overrightarrow{O B}-\overrightarrow{O A} \\ &\overrightarrow{A B}=3 \vec{\imath}+2 \hat{\jmath}+6 \hat{k} \\ &\overrightarrow{A B}=\sqrt{9+4+36} \\ &\overrightarrow{A B}=\sqrt{49} \\ &\overrightarrow{A B}=7 \end{aligned}

\begin{aligned} &\overrightarrow{B A}=\overrightarrow{O A}-\overrightarrow{O B} \\ &\overrightarrow{B A}=-3 \vec{\imath}+2 \hat{\jmath}-6 \hat{k} \\ &\overrightarrow{B A}=\sqrt{9+4+36} \\ &\overrightarrow{B A}=\sqrt{49} \\ &\overrightarrow{B A}=7 \\ &\overrightarrow{B C}=\overrightarrow{O C}-\overrightarrow{O B} \end{aligned}

\begin{aligned} &\overrightarrow{B C}=2 \vec{\imath}+6 \hat{\jmath}-3 \hat{k} \\ &\overrightarrow{B C}=\sqrt{4+36+9} \\ &\overrightarrow{B C}=\sqrt{49} \\ &\overrightarrow{B C}=7 \end{aligned}

\begin{aligned} &\overrightarrow{C B}=\overrightarrow{O B}-\overrightarrow{O C} \\ &\overrightarrow{C B}=-2 \vec{\imath}-6 \hat{\jmath}+3 \hat{k} \\ &\overrightarrow{C B}=\sqrt{4+36+9} \\ &\overrightarrow{C B}=\sqrt{49} \\ &\overrightarrow{C B}=7 \end{aligned}

\begin{aligned} &\overrightarrow{C A}=\overrightarrow{O A}-\overrightarrow{O C} \\ &\overrightarrow{C A}=-5 \vec{l}-8 \hat{j}-3 \hat{k} \\ &\overrightarrow{C A}=\sqrt{25+64+9} \\ &\overrightarrow{C A}=\sqrt{98} \\ &\overrightarrow{C A}=7 \sqrt{2} \end{aligned}

\begin{aligned} &\overrightarrow{A C}=\overrightarrow{O C}-\overrightarrow{O A} \\ &\overrightarrow{A C}=5 \vec{\imath}+8 \hat{\jmath}+3 \hat{k} \\ &\overrightarrow{A C}=\sqrt{25+64+9} \\ &\overrightarrow{A C}=\sqrt{98} \\ &\overrightarrow{A C}=7 \sqrt{2} \end{aligned}

\begin{aligned} &\operatorname{Cos} A=\frac{\overrightarrow{A B} \cdot \overrightarrow{A C}}{|\overrightarrow{A B}||\overrightarrow{A C}|} \\\\ &\operatorname{Cos} A=\frac{15+16+18}{(7)(7 \sqrt{2})} \\\\ &\operatorname{Cos} A=\frac{49}{49 \sqrt{2}} \\\\ &\operatorname{Cos} A=\frac{1}{\sqrt{2}} \end{aligned}

\begin{aligned} &A=\operatorname{Cos}^{-1}\left(\frac{1}{\sqrt{2}}\right) \\ &A=\frac{\pi}{4} \\ &\operatorname{Cos} B=\frac{\overrightarrow{B A} \cdot \overrightarrow{B C}}{|\overrightarrow{B A}||\overrightarrow{B C}|} \end{aligned}

\begin{aligned} &\operatorname{Cos} B=\frac{-6-12+18}{(7)(7)} \\ &\operatorname{Cos} B=\frac{0}{49} \\ &\operatorname{Cos} B=0 \\ &B=\operatorname{Cos}^{-1}(0) \\ &B=\frac{\pi}{2} \end{aligned}

\begin{aligned} &\operatorname{Cos} C=\frac{\overrightarrow{C B} \cdot \overrightarrow{C A}}{|\overrightarrow{C B}||\overrightarrow{C A}|} \\ &\operatorname{Cos} C=\frac{10+48-9}{(7)(7 \sqrt{2})} \\ &\operatorname{Cos} C=\frac{49}{49 \sqrt{2}} \end{aligned}

\begin{aligned} &\operatorname{Cos} C=\frac{1}{\sqrt{2}} \\ &C=\operatorname{Cos}^{-1}\left(\frac{1}{\sqrt{2}}\right) \\ &C=\frac{\pi}{4} \end{aligned}

Posted by

infoexpert21

View full answer

Crack CUET with india's "Best Teachers"

  • HD Video Lectures
  • Unlimited Mock Tests
  • Faculty Support
cuet_ads

Similar Questions

Trending Articles/News

anam-khan

Board Exam Time Table 2025 Live: UP Board exams from February 24; CBSE, BSEB date sheet soon
anam-khan

CBSE Date Sheet 2025 Live: Class 10, 12 board exam dates soon; syllabus, sample papers
anam-khan

Extra time in CBSE exams for students with type 1 diabetes: Kerala SHRC seeks report on plea

Latest Question