calculus - Maximize the area of an isosceles triangle bounded by a circle

Maximize the area of an isosceles triangle (let the smallest of the triangle's three angles = $2\theta$)

Triangle is bounded by a circle with radius $R$

Find angle $\theta$ which maximizes the area of the bounded triangle

Drew this out with $2\theta$ vertex pointing upward

Drew lines from center of the circle out to each vertex and noted that the angle directly below $2\theta$ (at center of circle) = $4\theta$

Next steps: possibly finding $\sin(2\theta)$ and $\cos(2\theta)?$ Not sure where to go from here. Any help welcomed.