Bonjour,
1) cos²(7π/12) = 1 - sin²(7π/12)
= 1 - [(√2 + √6)/4]²
= 1 - (2 + 6 + 2√2√6)/16
= (16 - 8 - 2√2√6)/16
= (4 - √2√6)/8
2) cos(7π/12) = √[(4 - √2√6)/8]
= √[(4 - √2√6)]/(2√2)
= √(2/√2 - √6/2)
= √(√2/2 - √6/2)
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Bonjour,
1) cos²(7π/12) = 1 - sin²(7π/12)
= 1 - [(√2 + √6)/4]²
= 1 - (2 + 6 + 2√2√6)/16
= (16 - 8 - 2√2√6)/16
= (4 - √2√6)/8
2) cos(7π/12) = √[(4 - √2√6)/8]
= √[(4 - √2√6)]/(2√2)
= √(2/√2 - √6/2)
= √(√2/2 - √6/2)