Use the trapezium rule with 3 strips to estimate the value of

${\int }_0^{\pi }2\cos \left(\frac{x}{2}\right)dx$

Give your answer to four decimal places.

Find the exact value of ${\int }_0^{\pi }2\cos \left(\frac{x}{2}\right)dx$.

Hence find the percentage error in the estimate found in part (a), giving your answer to three significant figures.