Figure 1 below shows the right-angled triangle ABCABCABC, in which the angle at C C\,C is a right angle and AB=5AB = 5AB=5 cm.
The angle BAC BAC\,BAC is θ\thetaθ, where θ \theta\,θ is measured in radians.
Given that θ \theta\,θ is small, show that AC≈5−5θ22\displaystyle AC \approx 5 - \frac{5\theta^2}{2}AC≈5−25θ2.
Hence find the length of AC AC\,AC when θ=0.1\theta = 0.1θ=0.1, giving your answer to four decimal places.