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counting and probability intermediate
Problem
Two real numbers are chosen at random between and What is the probability that the sum of their squares is no more than Express your answer as a common fraction in terms of .
Solution
We let the two numbers be and . The set of all possible pairs satisfy the inequalities and ; we can graph these points as a square on the plane with vertices and . This square has area
We want to find the area of the set of points which also satisfies . The set of ordered pairs that satisfy this inequality is a circle with radius centered at the origin.
The overlap between the circle and the square is the quarter-circle in the first quadrant with radius This region has area .
Thus, the desired probability is .
We want to find the area of the set of points which also satisfies . The set of ordered pairs that satisfy this inequality is a circle with radius centered at the origin.
The overlap between the circle and the square is the quarter-circle in the first quadrant with radius This region has area .
Thus, the desired probability is .
Final answer
\frac{\pi}{4}