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```
Prove that, (cos π/7) *(cos 3π/7) *(cos 5π/7) are the roots of the equation 8x 2 -4x 2 -4x+1=0
Prove that, (cos π/7) *(cos 3π/7) *(cos 5π/7) are the roots of the equation 8x2-4x2-4x+1=0

```
2 years ago

Arun
25768 Points
```							Dear Surya As we see that cos(π/7) + cos(3π/7) + cos(5π/7) Multuiply and divide by 2sin(π/7) = 1/2sin(π/7) [ 2sin(π/7)cos(π/7) + 2sin(π/7)cos(3π/7) + 2sin(π/7)cos(5π/7) ] Use the following sin(2A) = 2sinAcosA 2sinAcosB = sin(A+B) + sin(A-B) = 1/2sin(π/7) [ sin(2π/7) + sin(π/7+3π/7) + sin(π/7-3π/7) + sin(π/7+5π/7) + sin(π/7-5π/7) ] = 1/2sin(π/7) [ sin(2π/7) + sin(4π/7) + sin(-2π/7) + sin(6π/7) + sin(-4π/7) ] = 1/2sin(π/7) [ sin(2π/7) + sin(4π/7) - sin(2π/7) + sin(6π/7) - sin(4π/7) ] = 1/2sin(π/7) [sin(6π/7)] = 1/2sin(π/7) [sin(π - π/7)] = [sin(π/7)]/2sin(π/7) = ½ hence these are the roots
```
2 years ago
Surya
14 Points
```							It is not addition its multiplicationProve that, (cos π/7) (cos 3π/7) (cos 5π/7) are the roots of the equation 8x2-4x2-4x+1=0Pls solve this step by step.... Fast...
```
2 years ago
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### Course Features

• 31 Video Lectures
• Revision Notes
• Test paper with Video Solution
• Mind Map
• Study Planner
• NCERT Solutions
• Discussion Forum
• Previous Year Exam Questions