Solution-
We can solve this problem by using the concept of slope.
Slope of a line joining two points A (x1,y1) and B (x2,y2) is given by-
slope of AB= (y2-y1)÷(x2-x1)
We have given the vertices of a triangle as D(-4,1), E(3,-1) and F(-1,-4).
∴ slope of line joining D and E= (-1-1)÷(3-(-4))= -2/7
slope of line joining D and F= (-4-1)÷(-1-(-4))= -5/3
and slope of line joining E and F= (-4-(-1))÷(-1-3)= 3/4
∵ Two lines are perpendicular to each other if product of their slopes= -1
Statement 1 is wrong because, (slope of DE)×(slope of EF)=(-2/7)×(3/4)=-3/14≠ -1
Statement 2 is wrong because, (slope of DE)×(slope of DF)=(-2/7)×(-5/3) =10/21≠ -1
Statement 3 is wrong because,(slope of DF)×(slope of EF)=(-5/3)×(3/4)= -5/4≠ -1
∴Statement 4 is correct.
