1.

Let cosA+cosB=x,cos2A+cos2B=y,cos3A+cos3B=z,then which of the following is true

Answer»

`cos^(2)A+cos^(2)B=1+ y/2`
`1/4(2X^(2)-y-2)=cosAcosB`
`2x^(2)+z=3x(1+y)`
`xyz=0AA A, BepsilonR`

Solution :`X^(2)=cos^(2)A+cos^(2)B+2cosA.cosB`
`y=2(cos^(2)A+cos^(2)B)-2`
`:.cos^(2)A+cos^(2)B=1+y/2`
`:' cos A.cosBB=1/4(2x^(2)-y-2)` and `z=-2x^(3)+3xy+3x`
`:.2x^(3)+z=3x(y+1)` ltbrogt `xyz=0AA A` and `B` is not true


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