Set a = {an isosceles triangle with 2 sides and 30 angles}, then the number of subsets of set a is? And the answer is 16

Set a = {an isosceles triangle with 2 sides and 30 angles}, then the number of subsets of set a is? And the answer is 16

4
Set a has two elements
{1} the bottom angle is 30 ° and the bottom or adjacent edge is 2
2. The top angle is 30 ° and the bottom or adjacent edge is 2}
Number of subsets 2 ^ 2 = 4
The last 2 refers to the number of elements
The formula for finding the number of subsets of a set 2 ^ x
X is the number of elements
Then (2 ^ x) - 1 except empty set

Is the set {x | x ^ 2 + 4x = 0} x = 0, - 4 empty set its subset? Why?

An empty set is a subset of an arbitrary set, which is determined by its concept

Using description method: how to solve the set of roots of the square of X - 4x + 3 = 0

Just {x | x ^ 2-4x + 3 = 0}
You can also solve two, and write X in the form of {x1, X2}