Let set I = {1,2,3,4,5,6}, set a be contained in I, and set B be contained in I. If a contains three elements, B contains at least two elements, and all books in B are not less than the largest number in a, then how many groups of sets a and B satisfy the condition?

Let set I = {1,2,3,4,5,6}, set a be contained in I, and set B be contained in I. If a contains three elements, B contains at least two elements, and all books in B are not less than the largest number in a, then how many groups of sets a and B satisfy the condition?

Firstly, when the maximum element in a is at least 3a and the maximum element in a is 6, B does not exist. When the maximum element in a is 5, B is unique and {5,6}. At this time, there are six possibilities of C (4,2) = in a set. When the maximum element in a is 4, B may be {4,5}, {4,6}, {5,6}, {4,5,6}. The formula is C (3,2) + C (3,3) = 4, while a has three possibilities of C (3,2) = 4

Write the set of the following numbers (1) y = sin 30 °, sin 45 °, cos 45 ° sin 60 °
(2)y=sinAcosA,A=30°,45°,60°
（3）y=sinαcosβ,α,β∈（30°,45°,60°）

(1) {1/2,√2/2,√3/2}
(2) {1/2,√3/4}
(3) {1/4,3/4,1/2,√2/4,√3/4,√6/4}

+-Root sign (sin75 ° cos75 °) = + - root sign (sin150 ° / 2)
Why is this step

sin75°cos75°=sin150°/2
According to the formula sin2a = 2sinacosa
So + - radical (sin75 ° cos75 °) = + - radical (sin150 ° / 2)