Mathematics
Let be the area of the region ${\{(x,y)∈R^2:x^2+y^2≤21, y^2≤4x,x≥1}\}$. Then $\frac{1}{2}(Δ-21sin^{-1}\frac{2}{\sqrt7})$ is equal to
A
$\sqrt3 - \frac{2}{3}$
B
$2\sqrt3-\frac{2}{3}$
C
$2\sqrt3-\frac{1}{3}$
D
$\sqrt3-\frac{4}{3}$
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