[질문] 3점좌표알때삼각형넓이구하는공식은??10~나

사선공식1/2{(X2*Y1)+(X1*Y3)-(X1*Y2)+(X3*Y1)}삼각형ABC에서A(a,b),B(c,d),C(e,f)(a,b,c,d,e,f는정수)1/2{(c*b)+(a*f)-(a*d)+(e*a)}