2x + 4y – 8xy -1 =?

Simplify the following equation
$$ {\sqrt{(1-sin^{2}θ) ÷{(1-cos^{2}θ)}}}$$

5-[4-{3-(3-3-6)}] is equal to:

$$ { \sqrt{(0.798)^2+0.404×0.798+(0.202)^2}+1=?} $$

Assume that
$$\sqrt{3} = 3.605 \ (approximately)  $$
$$\sqrt{130} = 11.40 \ (approximately)  $$
Find the value of
$$\sqrt{1.3} + \sqrt{1300}+\sqrt{0.013}  $$

The smallest natural number, by which 3000 must be divided to make the quotient a perfect cube, is : 

Simplify : $$\sqrt{[(12.1)^2-(8.1)^2]÷[(0.25)^2+(0.25)(19.95)]} $$

What mathematical operation should come at the place of ‘?’ in the equation:
2 ? 6 – 12 ÷ 4 +2 =11.