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4.6 Summary (EMBGH)
 Distance between two points: \(d = \sqrt{(x_2  x_1)^2 + (y_2  y_1)^2}\)
 Gradient of a line between two points: \(m = \dfrac{y_2  y_1}{x_2  x_1}\)
 Midpoint of a line: \(M(x;y) = \left( \dfrac{x_1 + x_2}{2}; \dfrac{y_1 + y_2}{2} \right)\)
 Parallel lines: \(m_1 = m_2\)
 Perpendicular lines: \(m_1 \times m_2 = 1\)
 General form of a straight line equation: \(ax + by + c = 0\)
 Twopoint form of a straight line equation: \(\dfrac{y  y_1}{x  x_1} = \dfrac{y_2  y_1}{x_2  x_1}\)
 Gradient–point form of a straight line equation: \(y  y_1 = m(x  x_1)\)
 Gradient–intercept form of a straight line equation (standard form): \(y = mx + c\)
 Angle of inclination of a straight line: \(\theta\), the angle formed between the line and the positive \(x\)axis; \(m = \tan \theta\)
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