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Finding an Equation of a Line Perpendicular to a Given Line

To formulate the equation of a line that is perpendicular to a given line and passes through a specific coordinate point, apply this five-step algebraic procedure: 1. Find the slope of the original line. If needed, manipulate the given equation into slope-intercept form, y=mx+by = mx + b, to explicitly identify the slope mm. 2. Determine the perpendicular slope. Because perpendicular lines possess slopes that are opposite reciprocals, find the new slope by taking the negative reciprocal of the original one (i.e., let m=1mm_{\perp} = -\frac{1}{m}). 3. Identify the given point. Note the specific coordinates (x1,y1)(x_1, y_1) through which the new perpendicular line must pass. 4. Substitute backward into the point-slope formula. Plug the computed perpendicular slope and the given point coordinates into the template yy1=m(xx1)y - y_1 = m_{\perp}(x - x_1). 5. Convert to slope-intercept form. Simplify the equation and completely isolate the yy variable to write the final equation in the standard form y=mx+by = mx + b. By executing this negative reciprocal adjustment upfront, the routine ensures the resulting function intersects the original line at exactly a ninety-degree angle.

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Updated 2026-05-03

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