Finding the perimeter of triangles

Well theres not question to answer but if your asking how to find the area of a triange you do:

Step-by-step explanation:

1/2×b×h

B=base/length

H=height/width

He uses trigonometry.  In a right angled triangle, which we have here, we use one of the trig ratios sine, cosine or tangent to find  lengths of sides and/or measures of angles. The distance between the Moon and the Sun in this diagram is the hypotenuse of the triangle. We only need to know the measure of one angle ( other than the right angle) and another side to find this.
Here we use the cosine  :- cos x = adjacent / hypotenuse  so the hypotenuse = adjacent / cos x. = y / cos x.  We know what x and y are so its easy to find the hypotenuse.