I have a doubt in lightIt is written that if magnification has a plus sign then image is virtual and erect but if we look at case 2 of image formed by concave mirror I.e when object is at focus then the image formed is larger and real and inverted How is it possible

When the object is at focus the image formed isnt large. it is same size and inverted. For sign convection refer the graph’s sign. And if you are facing problems in understanding the nature of image watch animated video on youtube. Because all this is based on imagination.