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Question

Evaluate : 2/3(cos30^4-sin45^4)-3(sin²60-sec²45)+1/4cot²30

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Solution

Let x=2/3(cos30^4-sin45^4)-3(sin²60-sec²45)+1/4cot²30

Cos30=√3/2
Sin45=1/√2
Sin60=√3/2
Sec45=√2
Cot30=√3

Then,

x=2/3 * ( (√3/2)⁴ - (1/√2)⁴ ) - 3 * ( (√3/2)² - (√2)² ) + 1/4 * (√3)²

=2/3 ( 9/16 - 1/4 ) - 3 * ( 3/4 - 2 ) + 3/4

=(2/3 * 5/16)+ 15 / 4 + 3/4

=5 /24 + 9/2

=113/24

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