Finding the area of a triangle on a graph

[Count Duckula]

Here is the question: http://i259.photobucket.com/albums/hh299/the-real-guitar-hero/Capture_zpsf2b9cd28.png

part A = 3√5
b=y=2X+1
c=(0,1)
D is where I am confused. Area of triangle = (base x height)/2
from working out, line 2 cuts the x-axis at -1/2. line 1 cuts the x at 7. the height is 3. thus the area should be [(7.5*3)/2] = 11.25 . but the mark scheme says the answer is 7.5? which is length of the base! but the heck?This is just one of those small things that has confused the hell out of me >.<

 

[CompuChip]

The base of the triangle is PR, which does not have length 7 because P is not on the x-axis!
Similarly, the height of the triangle is PQ.

 

[Count Duckula]

Ugh. ok, so its, 3√5 * √5

 

[CompuChip]

Almost :)

Area of triangle = (base x height)/2