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