Alan

This is a geometric progression.  Here's a derivation for the n'th term:

Much the simplest Guest- well spotted!

Simplifying the ratio:

If it emits the power equally in all directions then by the time it reaches the Earth it will be spread out over the surface of a sphere of radius 19800 km.  The surface area of this is 4*pi*(1.98*10^7)^2 m^2.  Divide the 20W by this area to get the power in Watts per square metre (it will be a very small number!).

Arrhenius equation.  Does this help?

Hyperbolic functions (sinh/cosh etc.) aren't intrinsically defined in terms of angles.

If it is parallel it has the same slope, so it will be of the form y = -1.8x + c where c is a constant.

To find c use the fact that when x = -10 y = 2 so that 2 = -1.8*(-10) + c or 2 = 18 + c so c = 2 - 18 or c = -16

The equation is therefore y = -1.8x - 16

If it's a result of a calculation just press = or Enter once more on the calculator on the home page here.  If you enter a decimal and press = it will generally display a fraction.

Just divide 96.55 by 100 to turn it into a decimal.

Because sine takes values between -1 and  +1.  There is no angle for which the sine is bigger than 1.