Math Problem Statement

Find the y-intercept of the straight line which passes through the points (3, 4) and (1, -8).

Solution

To solve this problem, we need to determine the equation of the line passing through the points (3,4)(3, 4) and (1,8)(1, -8) and then find its yy-intercept.

Step 1: Find the Slope (Gradient) of the Line

The slope mm between two points (x1,y1)(x_1, y_1) and (x2,y2)(x_2, y_2) is given by: m=y2y1x2x1m = \frac{y_2 - y_1}{x_2 - x_1} Substituting the points (3,4)(3, 4) and (1,8)(1, -8): m=8413=122=6m = \frac{-8 - 4}{1 - 3} = \frac{-12}{-2} = 6

Step 2: Use the Point-Slope Form to Find the Equation of the Line

The equation of a line with slope mm passing through a point (x1,y1)(x_1, y_1) is: yy1=m(xx1)y - y_1 = m(x - x_1) Using point (3,4)(3, 4) and m=6m = 6: y4=6(x3)y - 4 = 6(x - 3) Expanding this: y4=6x18y - 4 = 6x - 18 y=6x14y = 6x - 14

Step 3: Identify the yy-Intercept

The yy-intercept occurs where x=0x = 0. In the equation y=6x14y = 6x - 14, substituting x=0x = 0 gives: y=6(0)14=14y = 6(0) - 14 = -14

Conclusion

The yy-intercept is 14-14.

Answer

The correct option is: A) -14

Would you like more details on any part of the solution? Here are some related questions to further explore:

  1. How do you find the slope of a line given two points?
  2. What is the point-slope form of a line, and how is it used?
  3. How can you verify the yy-intercept using different methods?
  4. What does the yy-intercept represent in a linear equation?
  5. How would the equation change if we had different points?

Tip: Always substitute the values back into the original points to verify the line equation is correct.

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Math Problem Analysis

Mathematical Concepts

Algebra
Coordinate Geometry
Linear Equations

Formulas

Slope formula: m = (y2 - y1) / (x2 - x1)
Point-slope form of a line: y - y1 = m(x - x1)
Slope-intercept form of a line: y = mx + b

Theorems

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Suitable Grade Level

Grades 9-11