How to find the cosine of dihedral angle

First, find the absolute value of cosine of the included angle between the normal vectors of two planes. If the dihedral angle is acute, it is positive, and if it is obtuse, it is negative.

Solution: Let the normal vector of Qu bread be n→=(x, y, 1).

Then √du3/2*x+3/2*y+√3=0.

4y=0

The solution is n → = (-2,0, 1)

Let the dihedral angle P-AC-B be θ, and we get

cosθ= cos & lt； n →, PB→& gt；

=(2√3+0+0)/[√(4+0+ 1)*√(3+ 1+0)]

=2√3/2√5

=√ 15/5

Extended data:

Chord value is the value that the length of the opposite side in a right triangle is greater than the length of the hypotenuse. The sine value of any acute angle is equal to the cosine value of other angles, and the cosine value of any acute angle is equal to the sine value of other angles, which is usually represented by the symbol sin. Sinθ can also be understood as the ratio of the area of a unit isosceles triangle with the vertex angle θ to the area of a unit isosceles right triangle.

sin30 = 1╱2

sin45 =√2╱2

sin60 =√3╱2

sin90 = 1

sin 180 =0

sin0 =0

sin270 =- 1

Baidu Encyclopedia-Sine Value