Solution pls

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Hey so this is my first post so Im not really sure how this goes but basically for this question, you need to have the prior knowledge that when there is a right angle triangle the area will be the greatest than from any other degree. So when the first point on the semi circle and the 4th point make a triangle it is a right angle triangle. And so when we find the area of this we get x as the area of the triangle. (1/2*square root 2x*square root 2x as the radius is square root 2x) we can then see that for thr area of the triangle to be less than x we need it to not be a right angle triangle. As point 1 on the semi circle and point 7 cant even make a triangle, there are 5 different triangles to be made by each point out of which 1 triangle will have an area x. So the probability of a triangle being less than x is 4/5