3 and 4 .Determinants and Matrices
medium

જો $F(x)=\left[\begin{array}{ccc}\cos x & -\sin x & 0 \\ \sin x & \cos x & 0 \\ 0 & 0 & 1\end{array}\right],$ હોય, તો દર્શાવો કે $F(x) F(y)=F(x+y)$

Option A
Option B
Option C
Option D

Solution

$F(x)=\left[\begin{array}{ccc}\cos x & -\sin x & 0 \\ \sin x & \cos x & 0 \\ 0 & 0 & 1\end{array}\right]$,   $F(y)=\left[\begin{array}{ccc}\cos y & -\sin y & 0 \\ \sin y & \cos y & 0 \\ 0 & 0 & 1\end{array}\right]$

$R.H.S:$   $F(x+y)=\left[\begin{array}{ccc}\cos (x+y) & -\sin (x+y) & 0 \\ \sin (x+y) & \cos (x+y) & 0 \\ 0 & 0 & 1\end{array}\right]$

$L.H.S:$  $F(x)$  $F(y)$

$ = \left[ {\begin{array}{*{20}{c}}
  {\cos x}&{ – \sin x}&0 \\ 
  {\sin x}&{\cos x}&0 \\ 
  0&0&1 
\end{array}} \right]$ $\left[ {\begin{array}{*{20}{c}}
  {\cos y}&{ – \sin y}&0 \\ 
  {\sin y}&{\cos y}&0 \\ 
  0&0&1 
\end{array}} \right]$

$=\left[\begin{array}{ccc}
\cos x \cos y-\sin x \sin y+0 & -\cos x \sin y-\sin x \cos y+0 & 0 \\
\sin x \cos y+\cos x \sin y+0 & -\sin x \sin y+\cos x \cos y+0 & 0 \\
0 & 0 & 0
\end{array}\right]$

$=\left[\begin{array}{ccc}\cos (x+y) & -\sin (x+y) & 0 \\ \sin (x+y) & \cos (x+y) & 0 \\ 0 & 0 & 1\end{array}\right]$

$=F(x+y)$

$\therefore   $  $F(x) F(y)=F(x+y)$

Standard 12
Mathematics

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