Here is an example of Cassegrain telescope: Parallel rays from a distant object get reflected by the concave mirror forming an image at its focus behind the convex mirror. This image acts as a virtual object for the convex mirror, and it forms a real image in front. Let's apply mirror equation for this convex mirror to find the distance at which final image is formed.
1/v + 1/u = 1/f
u = + 90; f= +70;
Therefore, 'v' comes out to be +315 cm. I am troubled to see this positive sign in image's distance, would not this mean that the image is formed to the left of convex mirror? Does sign convention fail in this case? Or have I made some fatal mistake?
The exact question statement goes like this: