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Find the coordinates of the point P which is three-fourth of the way from A(3, 1) to B(-2, 5).

Section Formula

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Answer

Coordinates of A(3, 1) and B(-2, 5).

Let P divides AB in ratio m1 : m2. Given P lies on AB such that,

AP = 34\dfrac{3}{4}AB = 34\dfrac{3}{4}(AP + PB)
⇒ 4AP = 3AP + 3PB
⇒ 4AP - 3AP = 3PB
⇒ AP = 3PB
⇒ AP : PB = 3 : 1.

∴ m1 : m2 = 3 : 1.

Let coordinates of P be (x, y). By section formula,

x=m1x2+m2x1m1+m2=(3×(2)+1×3)3+1=6+34=34.x = \dfrac{m1x2 + m2x1}{m1 + m2} \\[1em] = \dfrac{(3 \times (-2) + 1 \times 3)}{3 + 1} \\[1em] = \dfrac{-6 + 3}{4} \\[1em] = -\dfrac{3}{4}.

Similarly applying section formula we get y-coordinate,

y=m1y2+m2y1m1+m2=3×5+1×13+1=15+14=164=4.y = \dfrac{m1y2 + m2y1}{m1 + m2} \\[1em] = \dfrac{3 \times 5 + 1 \times 1}{3 + 1} \\[1em] = \dfrac{15 + 1}{4} \\[1em] = \dfrac{16}{4} \\[1em] = 4.

∴ P = (34,4).\Big(-\dfrac{3}{4}, 4\Big).

Hence, coordinates of P are (34,4).\Big(-\dfrac{3}{4}, 4\Big).

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