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Circumference of parametric ellipse?

Ok so I've got this question that I dunno how to do the first part.

An ellipse has parametric equations

x=cos(t), y=\frac{\sqrt(3)sin(t)}{2}

.

Show that the length of its circumference is given by

2\int_0^\frac{\pi}{2}(\sqrt(3+sin^2(t)) dt

(thats the part i dont understand)

The integral cannot be evaluated in terms of elementary functions. USe the trapezium rule with interval-halving to evaluate it to 6dp. (<- I can do this part)
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I've never done anything like the first part before :s

I found a formula