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Prove that: 8cos^3pi/9-\ 6cospi/9=1....

Prove that: `8cos^3pi/9-\ 6cospi/9=1.`

Text Solution

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Given,
`8cos^3(pi/9)−6cos(pi/9)`
`=2cos(pi/9)xx4cos^2(pi/9)−2xx3cos(pi/9)`
`=2cos(pi/9)[4cos^2(pi/9)−3]`
`=2xxcos(pi/3)`
`=2xx1/2`
`=1`
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