1. ## Express Y coordiante

Hello
Help with the question on my drawing please?
its a rectangle in isoceles right triangle

Hello
Help with the question on my drawing please?
its a rectangle in isoceles right triangle
If the triangles are isosceles and right-angled, then B is the point $\displaystyle (0,1)$. So the equation of AB is
$\displaystyle x+y=1$
So, making $\displaystyle y$ the subject:
$\displaystyle y = 1-x$
which gives the value of $\displaystyle y$ at the point P.

3. Thanks
I got that but I was no sure if it was correct

but I done it this way y-y1=m(x-x1)
1-x=0(1-x)
would it be correct to write it like this also?

Thanks
I got that but I was no sure if it was correct

but I done it this way y-y1=m(x-x1)
You can certainly use
$\displaystyle y-y_1=m(x-x_1)$
to get the equation of the line. Using
$\displaystyle x_1=1,\;y_1=0$ and $\displaystyle m = -1$
gives
$\displaystyle y-0=-1(x-1)$

$\displaystyle \Rightarrow y = 1-x$
But this line doesn't make sense, and is not correct: