Question

plz answer I am in great hurry...
one question please answer in the question no 7 how can we know that here image is convex..?
as it is asking name kind of lens so how can we know that lens is convex here??
please answer​

Answer 1

using lens formula 1/F=1/v-1/u, here u= -45cm and v= 95cm ( here mentioned that screen placed other side so if u is negative so v positive), 1/F=1/90-(-1/45), 1/F= 1/90+1/45, 1/F= 1+2/90, 1/F= 3/90, 1/F=1/30 means F is +30cm and focal length of convex is positive so it is convex lens then magnification = v/u , m=90/-45 , m= -2