Radius of Curvature of Mirror Question. Check my Work!?

Question

question: a concave makeup mirror is designed so the virtual image it produces is twice the size of the object when the distance between the object and the mirror is 14 cm. what is the radius of curvature of the mirror?

approach: i took half of do and got 7 cm. then, i plugged in numbers into 1/f = 1/do + 1/di with variables di = 14 cm, do = 7m. I got f = 4.7. I took half of that to get radius and got R = 2.3 cm.

my main question is...did i half or multiply the right number? is this right?

Answer 1

You should multiply f by 2. Radius is twice the focal distance.