Arectangle is inscribed in a circle of radius r. if the rectangle has length 3x, write the area of the rectangle as the product of two function in terms of x and r

Based on the given condition, since the rectangle is inscribed in a circle given the length to be 3x, the width can be approximated by taking the right triangle formed by the radius and the w/2, sin 45 = w/2/r, which is equal to w = 2r sin45, therefore the Area of the inscribed rectangle = LxW = (3x)(2rsin45)