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Sec 15 = 1/cos 15

so cos 15 = cos(45 - 30)= cos45cos30 + sin45sin30

=(1/√2)(√3/2) + (1/√2)(1/2)

= (√3 + 1)/(2√2)

so 1/cos 15= (2√2) / (√3 + 1)

sec 15 = (2√2) / (√3 + 1)

so cos 15 = cos(45 - 30)= cos45cos30 + sin45sin30

=(1/√2)(√3/2) + (1/√2)(1/2)

= (√3 + 1)/(2√2)

so 1/cos 15= (2√2) / (√3 + 1)

sec 15 = (2√2) / (√3 + 1)