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Write down the equation of the line whose gradient is 32\dfrac{3}{2} and which passes through P, where P divides the line segment joining A(-2, 6) and B(3, -4) in the ratio 2 : 3.

Straight Line Eq

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Answer

By section-formula,

P = (m1x2+m2x1m1+m2,m1y2+m2y1m1+m2)\Big(\dfrac{m1x2 + m2x1}{m1 + m2}, \dfrac{m1y2 + m2y1}{m1 + m2}\Big)

Substituting values we get,

P=(2×3+3×22+3,2×4+3×62+3)=(6+(6)5,8+185)=(05,105)=(0,2).P = \Big(\dfrac{2 \times 3 + 3 \times -2}{2 + 3}, \dfrac{2 \times -4 + 3 \times 6}{2 + 3}\Big) \\[1em] = \Big(\dfrac{6 + (-6)}{5}, \dfrac{-8 + 18}{5}\Big) \\[1em] = \Big(\dfrac{0}{5}, \dfrac{10}{5}\Big) \\[1em] = (0, 2).

By point-slope form,

Equation of line with slope = 32\dfrac{3}{2} and passing through (0, 2) is :

⇒ y - y1 = m(x - x1)

⇒ y - 2 = 32\dfrac{3}{2}(x - 0)

⇒ 2(y - 2) = 3x

⇒ 2y - 4 = 3x

⇒ 2y = 3x + 4.

Hence, equation of required line is 2y = 3x + 4.

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