What is the use of the Heron's Formula?
If you have homework that involves solving an area of a triangle but there's no angle you're unsure if the typical A=1/2*bh will give you a correct answer, then you can use Heron's Formula to get a better answer. This is a really handy formula if you have no other idea how can approach a problem with complex figures.
What is the difference between using the actual value of pi and using only 3.1416?
There's not much difference but you will notice a discrepancy with the decimal values. The actual value of pi very long but gives a more accurate answer especially when solving for circles. When you use 3.1416, it will still yield almost the same answer. For example: 3 x pi = 9.424777961; whereas 3 x 3.1416 = 9.4248 See the small difference in the decimal but doesn't create a very big impact on the answer. If you'll round it up to two decimal places, they will both just be simplified as 9.42.
Why are you interested in learning English?
I am very interested in learning the language because it is universal and easy to understand. Native languages are fine to learn as well but English is widely-spoken by many and it can give me great advantages. If I have to plans to go abroad or if I just want a casual conversation with someone, I can easily express myself and understand what the other person is talking about.