Problem:
A vertical line divides the triangle with vertices (0,0),(1,1) and (9,1) in the xy-plane into two regions of equal area. The equation of the line is x=
Answer Choices:
A. 2.5
B. 3.0
C. 3.5
D. 4.0
E. 4.5
Solution:
In the adjoining figure, ABC is the given triangle and x=a is the dividing line. Since Area β³ABC=21β(I)(8)=4, the two regions must each have area 2. Since the portion of β³ABC to the left of the vertical line through vertex A has area less than Area β³ABF=21β, the line x=a is indeed right of A as shown. Since the equation of the line BC is y=9xβ,E is (a, 9aβ).
Thus Area β³DEC=2=21β(1β9aβ)(9βa),or (9βa)2=36. Then 9βa=Β±6, and a=15 or 3. Since the line x=a must intersect β³ABC,x=3.