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The line segment joining A(2, 3) and B(6, -5) is intersected by x-axis at a point K. Write down the ordinate of the point K. Hence, find the ratio in which K divides AB. Also find the coordinates of point K.

Section Formula

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Answer

Let the coordinates of K be (x, 0) as it intersects x-axis. Let point K divides the line segment joining the points
A(2, 3) and B(6, -5) in the ratio m1 : m2.

By section formula, y-coordinate = (m1y2+m2y1m1+m2)\Big(\dfrac{m1y2 + m2y1}{m1 + m2}\Big)

Putting value in above formula we get,

0=m1×(5)+m2×3m1+m20=5m1+3m25m1=3m2m1m2=35\Rightarrow 0 = \dfrac{m1 \times (-5) + m2 \times 3}{m1 + m2} \\[1em] \Rightarrow 0 = -5m1 + 3m2 \\[1em] \Rightarrow 5m1 = 3m2 \\[1em] \Rightarrow \dfrac{m1}{m2} = \dfrac{3}{5}

Now for x coordinate by section formula we get,

x=m1x2+m2x1m1+m2=3×6+5×23+5=18+108=288=72.x = \dfrac{m1x2 + m2x1}{m1 + m2} \\[1em] = \dfrac{3 \times 6 + 5 \times 2}{3 + 5} \\[1em] = \dfrac{18 + 10}{8} \\[1em] = \dfrac{28}{8} \\[1em] = \dfrac{7}{2}.

∴ K = (x, 0) = (72,0).\Big(\dfrac{7}{2}, 0\Big).

Hence, the coordinates of K are (72,0)\Big(\dfrac{7}{2}, 0\Big) and the ratio is 3 : 5.

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