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The points A(-1,2), B(x,y) and C(4,5) are such that BA=BC. Find a linear relation between x and y.
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This problem has a nice Algebra solution.
The square of the length of AB is
|AB|^2 = (x-(-1))^2 + (y-2)^2 = (x+1)^2 + (y-2)^2 = x^2 + 2x + 1 + y^2 - 4y + 4 = x^2 + 2x + y^2 - 4y + 5.
The square of the length of BC is
|BC|^2 = (x-4)^2 + (y-5)^2 = x^2 - 8x + 16 + y^2 - 10y + 25 = x^2 - 8x + y^2 - 10y + 41.
The condition |BA| = |BC| is the same as |AB|^2 = |BC|^2. It gives this equation
x^2 + 2x + y^2 - 4y + 5 = x^2 - 8x + y^2 - 10y + 41.
Combine like terms. The final equation is
10x + 6y = 36,
or
5x + 3y = 18,
or
y = . <<<---=== ANSWER
Solved.