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Coordinate Geometry (Hard)

Late AMC 10/12 through early AIME — dense computation.

Coordinate Geometry: core idea

Right-angle conditions.

Example problem: hint and answer

Find the area of the triangle (0,0),(8,0),(3,6)(0,0),(8,0),(3,6).

Hint: Translate the stated geometry into slopes, distances, or coordinates. Answer: 24.

Practice (9 problems — type your answers)

  • 1. A circle through (1,2),(7,2),(4,6)(1,2),(7,2),(4,6) has center (4,k)(4,k). Find kk.

  • 2. The line through (1,5),(5,1)(1,5),(5,1) meets y=2y=2 at (a,2)(a,2). Find aa.

  • 3. A square has adjacent vertices (1,1),(5,4)(1,1),(5,4). Find its area.

  • 4. Find the distance from (4,−3)(4,-3) to 3x+4y=03x+4y=0.

  • 5. The perpendicular bisector of (2,1),(8,5)(2,1),(8,5) meets y=0y=0 at (a,0)(a,0). Find aa.

  • 6. A line of slope −2-2 through (3,7)(3,7) meets the xx-axis at (a,0)(a,0). Find aa.

  • 7. Find the area of (0,0),(6,0),(8,3),(2,3)(0,0),(6,0),(8,3),(2,3).

  • 8. Lines x+y=8x+y=8 and 2x−y=12x-y=1 meet at (a,b)(a,b). Find abab.

  • 9. A circle centered at (3,−1)(3,-1) is tangent to the yy-axis. Find area/π/\pi.

Coordinate Geometry Practice Problems — Hard