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Explain Solution R.D.Sharma Class 12 Chapter 23 Scalar or Dot Products Exercise 23.1 Question 40 Maths Textbook Solution.

Answers (1)

Answer: Proved

Hints: You must know the rules of solving vectors.

Given:  If \vec{c}  is perpendicular to both \vec{a} and \vec{b} then prove that it is perpendicular to both \vec{a}+\vec{b}  and  \vec{a}-\vec{b}

Solution:  Given that \vec{c} is perpendicular to both \vec{a} and \vec{b}

\Rightarrow \vec{c}.\vec{a}=0 and \Rightarrow \vec{c}.\vec{b}=0

Now,

\begin{aligned} &\Rightarrow \vec{c}(\vec{a}+\vec{b})=\vec{c} \cdot \vec{a}+\vec{c} \cdot \vec{b} \\\\ &\Rightarrow 0+0=0 \end{aligned}

So, \vec{c} is perpendicular to \vec{a}+\vec{b}

Again,

\begin{aligned} &\vec{c} \cdot(\vec{a}-\vec{b})=\vec{c} \cdot \vec{a}-\vec{c} \cdot \vec{b} \\ &\vec{c} \cdot(\vec{a}-\vec{b})=0-0 \\ &\vec{c} \cdot(\vec{a}-\vec{b})=0 \end{aligned}

So, \vec{c} is perpendicular to \vec{a}-\vec{b}

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