- #1

Andrax

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## Homework Statement

so we have a (D) Line (geometry) it's Cartesian equation is ax+by+c=0

we have an [itex]A[/itex]([itex]\alpha[/itex],[itex]\beta[/itex])

prove that the distance between the line(D) and the point A is

d=[itex]\frac{la\alpha+b\beta+cl}{\sqrt{a^2+b^2}}[/itex]

## Homework Equations

## The Attempt at a Solution

let every distance be a vector (sorry didn't find vectors in the latex reference)

AH h belongs to (D) and AH factors (D) so AH(a,b)

we also have n vector (-b,a)

we can say that the catersian equation of ah is -b(x-[itex]\alpha[/itex])+a(y-[itex]\beta[/itex])+c I am pretty musch stuck here now to get this \sqrt{a^2+b^2} we will probably use cos but ireally can't find how r we supposed to use it :( please help guys: