Need help with Simple harmonic motion (H2 Physics)

I decided to self study oscillation but I am confused on this part (not very sure how to explain it)

https://www.instagram.com/p/BHcrkxlBsvL/?taken-by=lolwerwdr

Why is it that for a small θ , sinθ = tanθ = θ?

https://www.instagram.com/p/BHcq0BRhvew/?taken-by=lolwerwdr

For CS Toh Qns 4(ii), I am also stucked on a similar question.

Thanks!

I've addressed your qn 4ii from cs toh physics practice qns book in the Physics questions thread. u can go check it out.

does Cstoh's physics practice qn book include worked solutions for the questions inside the book?