1.

If f(x) = `[(cos x , - sinx,0),(sinx,cosx,0),(0,0,1)]` then show f(x) . f(y) = f(x+y)

Answer» Here, `f(x) = [[cosx,-sinx,0],[sinx,cosx,0],[0,0,1]]`
`:. f(y) = [[cosy,-siny,0],[siny,cosy,0],[0,0,1]]`
`:.f(x+y) = [[cos(x+y),-sin(x+y),0],[sin(x+y),cos(x+y),0],[0,0,1]]`
Now,`L.H.S. = f(x)*f(y)`
`= [[cosx,-sinx,0],[sinx,cosx,0],[0,0,1]] [[cosy,-siny,0],[siny,cosy,0],[0,0,1]]`
`=[[cosxcosy-sinxsiny,-cosxsiny-sinxsiny,0],[sinxcosy+cosxsiny,-sinxsiny+cosxcosy,0],[0,0,1]]`
`=[[cos(x+y),-sin(x+y),0],[sin(x+y),cos(x+y),0],[0,0,1]]`
`=f(x+y) = R.H.S.`


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