# Practice for midterm: help on projection

Hi I have a midterm this friday, and our prof gave us this practice midterm, i got 6 of the 10 questions but couldnt do the last 4, could you please help me out in this question, i have no idea how to approach it, Thank you.

Consider the central projection in $\mathbb{R^3}$ with respect to point $O$ onto a plane $P$. Let $P_0$ be the plane parallel to $P$ and passing through the origin. Let $L_1, L_2$ be two parallel lines contained in a plane $C$.

a) Describe the images of $L_1$ and $L_2$ in $P$ if the planes $C$ and $P$ are not parallel.

b) Describe their images if the planes $P$ and $C$ are parallel. Justify your answer.

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 Seems $P_0$ is irrelevant to your question. If this is about projective geometry, you're probably used to a standard embedding of the drawing plane into $\mathbb R^3$. E.g. you'd usually add $z=1$ to all coordinates. Use that embedding for $P$ and think about whether the images of parallel lines will be parallel or not. – MvG Feb 9 at 4:01