Someone can just help me with this MATHS Problem

Q. If A(-5,7),B(-4,-5),C(-1,-6),D(4,5) are the vertices of a quadrilateral, find the area of the quadilateral ABCD?

I solved this by using coordinate gemotery area of triange finding method- 1/2[x1(y2-y3) + x2(y3-y1)+ x3(y1-y2)].
I divided the quadilateral into two triangles so that i can use the above formula to find the area of quadilateral(ar of quad=ar of triange 1 + area of triange 2)

When i named the four vertices of quadilateral clockwise "ABCD" and drew a diagonal it formed two triangles ABD & BCD.
I got the answer 72 sq units.This was the right answer given in my book.

But, while doing this question second time I just wrote triangle BCD as BDC while finding triangles area i got a completely different answer. For triange BDC -19 & for whole quadilateral 34. Please someone help me from this problem

Dude... U did everything right... What u did wrong is that considering the area as -19... U may have got the ans . As -19 but u while adding the areas of the triangle u will just have to consider it as +19 coz areas cannot be in -ve... Like take this as for example... When u take distance in geometry like for say from (-1) to (-5)... Although the distance is being measured in -ve x-axis... The distance will be +4 coz distance will always be measured in +ve... By -ve means that it is being measured in opposite direction to the +ve x-axis... Hope u understood.. Dost.. Bas adding karte waqt use + 19 pakar..
Ise best ans. Chuuna bhai... Thnx..

Area of ABCD= Area of triangle ABD+ Area of tringle BCD Apply Co ordinate geo.

= 1/2 -5 7 1 + 1/2 -4 -5 1
-4 -5 1 -1 -6 1
4 5 1 4 5 1 =1/2(144)=72