The most basic formula is, of course, the bottom multiplied by the height, from which we can deduce the formula: S=S=|AB||AC|sinA, that is, the product of two adjacent sides multiplied by the sine of the included angle. In fact, the sine of that side multiplied by the included angle is the height, which is the first formula. You also use this formula in this problem. At the same time, triangles also have this similar formula, which is equivalent to half of parallelogram, so it is S= 1/2|AB||AC|sinA.