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# Coordinates

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Points \$A,\$ \$B,\$ and \$C\$ are given in the coordinate plane. There exists a point \$Q\$ and a constant \$k\$ such that for any point \$P\$,
PA^2 + PB^2 + PC^2 = 3PQ^2 + k.
If \$A = (7,-11),\$ \$B = (10,13),\$ and \$C = (18,-22)\$, then find the constant k.

Jul 1, 2024

#1
+1261
+1

Let's set up some variables to solve this problem.

Let's first set that \(P = (x,y)\)

Now, from the problem, we can write the complicated equation of

\(PA^2 + PB^2 + PC^2 = (x-7)^2 + (y + 11)^2 + (x-10)^2 + (y-13)^2 + (x-18)^2 + ( y + 22)^2 \)

Now, we have to simplify this gigantic equation. By expanding and combining lots of like terms, we get that

\(3 x^2 - 70 x + 3 y^2 + 40 y + 1247 \\ 3 [ x^2 - 70/3 x + y^2 + 40/3 y ] + 1247\)

Now, we simplfy complete the square for x and y to achieve our x and y values for point Q, which will be crucial.

Completing the square, we have

\(3[ x^2 - 70/3 x + 4900/36 + y^2 + 40/3y + 1600/36 ] + 1247 - 4900/12 -1600/12 \\ 3 [ (x - 70/6]^2 + (y + 40/6)^2 ] + 2116 / 3\)

Now, from this, we can tell what Q has for their x and y value.

We have that Q = (70/6, -20/3)

Thus, we know that

\(k = 2116 / 3 \)

So 2116/3 is our final answer.

Thanks! :)

Jul 1, 2024

#1
+1261
+1

Let's set up some variables to solve this problem.

Let's first set that \(P = (x,y)\)

Now, from the problem, we can write the complicated equation of

\(PA^2 + PB^2 + PC^2 = (x-7)^2 + (y + 11)^2 + (x-10)^2 + (y-13)^2 + (x-18)^2 + ( y + 22)^2 \)

Now, we have to simplify this gigantic equation. By expanding and combining lots of like terms, we get that

\(3 x^2 - 70 x + 3 y^2 + 40 y + 1247 \\ 3 [ x^2 - 70/3 x + y^2 + 40/3 y ] + 1247\)

Now, we simplfy complete the square for x and y to achieve our x and y values for point Q, which will be crucial.

Completing the square, we have

\(3[ x^2 - 70/3 x + 4900/36 + y^2 + 40/3y + 1600/36 ] + 1247 - 4900/12 -1600/12 \\ 3 [ (x - 70/6]^2 + (y + 40/6)^2 ] + 2116 / 3\)

Now, from this, we can tell what Q has for their x and y value.

We have that Q = (70/6, -20/3)

Thus, we know that

\(k = 2116 / 3 \)

So 2116/3 is our final answer.

Thanks! :)

NotThatSmart Jul 1, 2024