1. Statement of the problem: Find the equation of the line in slope-intercept form that passes through the points $(-1, 7)$ and $(4, -8)$.
2. Formula: Use the slope formula $m = \frac{y_2 - y_1}{x_2 - x_1}$ and the slope-intercept form $y = mx + b$.
3. Important rules: Subtract coordinates in the same order, simplify fractions to lowest terms, and substitute a known point to solve for $b$.
4. Compute the slope step by step.
$$m = \frac{-8 - 7}{4 - (-1)} = \frac{-15}{5} = -3$$
5. Find the y-intercept by substituting one point into $y = mx + b$.
$$7 = -3(-1) + b \Rightarrow 7 = 3 + b \Rightarrow b = 4$$
6. Final equation and explanation: Therefore the line in slope-intercept form is $y = -3x + 4$.
7. Check with the other point: Substituting $(4, -8)$ gives
$$-8 = -3(4) + 4 = -12 + 4 = -8$$
8. Conclusion: The equation of the line is $y = -3x + 4$.
Line Equation
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