Alan

Yes, you're right Chris.

.

There is no general answer to this as it depends on the shape!  

However, if the shape is constructed of straight lines then chopping it up into a number of triangles is often a good start.

.

You can use the calculator to divide the weight by the number of centimetres.

.

Is N exactly divisible by 7?

Let N = 10n + a    where n and a are integers and a is in the units position.

Construct M = n - 2a   (i.e. twice the units value subtracted from what's left, where what's left is considered to be a number in its own right).

If M is exactly divisible by 7 then we can write  n - 2a = 7m  where m is an integer.

So n = 7m + 2a

In that case N = 10(7m + 2a) + a  or  N = 70m + 21a

So N/7 = 10m + 3a and since m and a are integers the resulting value of N/7 is an integer.  i.e. N is exactly divisible by 7 with no remainder.

.

Note that 90 is a common multiple rather than a common factor, Anonymous.

.

Factors of 45:   1, 3, 5, 9, 15, 45

Factors of 18:  1, 2, 3, 6, 9, 18

I'll leave you to select the common ones.

.

.

The prefix "m" usually stands for "milli" or one thousandth, so 45 mg is 45 milligrams or 45/1000 grams or 0.045 g

.

r*sin(θ) = 6*(r*cos(θ)²)

sin(θ) = 6*r*cos(θ)²

r = tan(θ)/(6*cos(θ))   or r = tan(θ)*sec(θ)/6

.

Cartesian coordinates (x, y) become polar coordinates (√(x² + y²), tan^-1(y/x))

.