
Recall that a circle of radius 2 centered at the origin has equation

where the positive root gives the top half of the circle in the x-y plane. The definite integral corresponds to the area of the right half of this top half. Since the area of a circle with radius

is

, it follows that the area of a quarter-circle would be

.
You have

, so the definite integral is equal to

.
Another way to verify this is to actually compute the integral. Let

, so that

. Now

Recall the half-angle identity for cosine:

This means the integral is equivalent to
The relationship between the legs and hypotenuse of a 45 45 90 triangle can be written as:
1: 1: square root 2
The axis of symmetry of this function is x = 1. I hope this helps!
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