Sign conventions of concave and convex lens​

Explanation:

The New Cartesian Sign Convention of Concave and Convex Lens

According to the sign convention, a convex lens focal length is positive, whereas a concave lens focal length is negative. The incident light always moves from left to right because the object is always on the lens's left side.

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answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.