Geometry · real student question

Find the distance between the points (1802, 139, -4524) and (1885, 132, -4592).

Question

Find the distance between

A=(1802,139,4524)andB=(1885,132,4592)A=(1802,\,139,\,-4524)\qquad\text{and}\qquad B=(1885,\,132,\,-4592)

Step-by-step solution

  1. Write the three-dimensional distance formula. It is the Pythagorean theorem applied twice:

    d=(x2x1)2+(y2y1)2+(z2z1)2d=\sqrt{\left(x_2-x_1\right)^2+\left(y_2-y_1\right)^2+\left(z_2-z_1\right)^2}

    Only the differences matter, so the large absolute values of the coordinates are irrelevant to the answer.

  2. Compute the three differences.

    Δx=18851802=83,Δy=132139=7,Δz=4592(4524)=68\Delta x=1885-1802=83,\qquad \Delta y=132-139=-7,\qquad \Delta z=-4592-(-4524)=-68

    The zz difference is the one to watch: subtracting a negative gives 4592+4524=68-4592+4524=-68.

  3. Square and add.

    832=6889,(7)2=49,(68)2=462483^2=6889,\qquad (-7)^2=49,\qquad (-68)^2=4624

    6889+49+4624=115626889+49+4624=11562

    Squaring removes the signs, so the direction of travel does not affect the distance.

  4. Take the square root and try to simplify.

    d=11562d=\sqrt{11562}

    Factoring, 11562=23414711562=2\cdot 3\cdot 41\cdot 47 — every prime appears to the first power, so there is no perfect-square factor to pull out. The radical is already in simplest form.

  5. Give the decimal value and sanity-check it.

    d=11562107.53d=\sqrt{11562}\approx 107.53

    The largest single difference is 8383, and the distance must exceed it but be less than the sum 83+7+68=15883+7+68=158; 107.53107.53 sits comfortably inside that window \checkmark. Squaring back, 107.532=11562.7107.53^2=11562.7, consistent to rounding.

Answer

d=11562107.53d=\sqrt{11562}\approx 107.53

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