Coordinate geometry application: Find the area (in square units) of the triangle formed by the three lines x = 4, y = 3, and 3x + 4y = 12. Clearly identify each pairwise intersection point and then compute the triangle's area.

Difficulty: Easy

Correct Answer: 6

Explanation:


Introduction / Context:
This problem uses straight-line graphs to form a triangle. The goal is to find the three vertices by intersecting the given lines and then compute the triangle's area. It tests core coordinate geometry skills: finding intersections and applying a basic area formula for a right triangle.



Given Data / Assumptions:

  • Lines: x = 4 (vertical), y = 3 (horizontal), and 3x + 4y = 12 (a slanted line).
  • All intersections are within the real plane.
  • Area is requested in square units.


Concept / Approach:
The intersections of x = 4 and y = 3 with 3x + 4y = 12 give two vertices on the axes. The third vertex is simply the intersection of x = 4 and y = 3. The area of a right triangle is (1/2) * base * height; here the legs will be horizontal and vertical, making the calculation straightforward.



Step-by-Step Solution:

Intersect x = 4 with 3x + 4y = 12 ⇒ 3(4) + 4y = 12 ⇒ 12 + 4y = 12 ⇒ y = 0, so A(4, 0).Intersect y = 3 with 3x + 4y = 12 ⇒ 3x + 12 = 12 ⇒ x = 0, so B(0, 3).Intersect x = 4 with y = 3 ⇒ C(4, 3).Segment BC is horizontal (length 4), segment CA is vertical (length 3), so triangle ABC is right-angled at C.Area = (1/2) * 4 * 3 = 6 square units.


Verification / Alternative check:
Plotting quickly shows the right angle at (4, 3) with legs along x and y directions. Shoelace formula also yields 6 if applied to (4,0), (0,3), (4,3).



Why Other Options Are Wrong:
12 and 8 correspond to using full rectangle areas (4*3) or mis-halving; 10 is an arbitrary miscalculation. The only correct area is 6.



Common Pitfalls:
Confusing which intersections lie on axes, or forgetting to take half the product of the perpendicular legs when computing the area.



Final Answer:
6

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