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Answer:
[tex]x^2 + 4x + y^2 +8y = 0[/tex]
Step-by-step explanation:
Given
[tex]A = (-1,-2)[/tex]
[tex]B = (2,4)[/tex]
[tex]AP:BP = 1 : 2[/tex]
Required
The locus of P
[tex]AP:BP = 1 : 2[/tex]
Express as fraction
[tex]\frac{AP}{BP} = \frac{1}{2}[/tex]
Cross multiply
[tex]2AP = BP[/tex]
Calculate AP and BP using the following distance formula:
[tex]d = \sqrt{(x - x_1)^2 + (y - y_1)^2}[/tex]
So, we have:
[tex]2 * \sqrt{(x - -1)^2 + (y - -2)^2} = \sqrt{(x - 2)^2 + (y - 4)^2}[/tex]
[tex]2 * \sqrt{(x +1)^2 + (y +2)^2} = \sqrt{(x - 2)^2 + (y - 4)^2}[/tex]
Take square of both sides
[tex]4 * [(x +1)^2 + (y +2)^2] = (x - 2)^2 + (y - 4)^2[/tex]
Evaluate all squares
[tex]4 * [x^2 + 2x + 1 + y^2 +4y + 4] = x^2 - 4x + 4 + y^2 - 8y + 16[/tex]
Collect and evaluate like terms
[tex]4 * [x^2 + 2x + y^2 +4y + 5] = x^2 - 4x + y^2 - 8y + 20[/tex]
Open brackets
[tex]4x^2 + 8x + 4y^2 +16y + 20 = x^2 - 4x + y^2 - 8y + 20[/tex]
Collect like terms
[tex]4x^2 - x^2 + 8x + 4x + 4y^2 -y^2 +16y + 8y + 20 - 20 = 0[/tex]
[tex]3x^2 + 12x + 3y^2 +24y = 0[/tex]
Divide through by 3
[tex]x^2 + 4x + y^2 +8y = 0[/tex]