Answer: 3x + 4y = 25.
- A 3x + 4y = 25
- B 4x + 3y = 25
- C 3x - 4y = 25
- D x + y = 7
Correct answer: A. 3x + 4y = 25
Explanation: Tangent to x² + y² = r² at (x<sub>1</sub>,y<sub>1</sub>) is xx<sub>1</sub> + yy<sub>1</sub> = r². Here: 3x + 4y = 25.
The slope of a line is the ratio of vertical change (rise) to horizontal change (run) between any two points on it - equivalently, the tangent of the angle θ the line makes with the positive x-axis.