May I know what's the method use below to find the area. I don't think I was taught by my teacher.

That's a method taught in A.Maths.Alternatively,you can find the lengths of AB and AC using the length formula.Then,find angle BAC using Cosine Rule.Then, area of triangle ABC = 1/2 × AB × AC× sin angle BAC.If you need the solution using this method,do let me know.Thks.