Answer:
Oligopoly
Explanation:
An oligopoly is the structure of the market that is characterized by the domination of a few firms or industries. Other small firms also operate in the same market, but the power concentration is associated with few firms only. Interdependency among the firms helps in planning and strategy making to introduce new ideas to increase the market activities. The competition in the market is reduced when a few of the firms dominate the market. It results in an increase in the price of commodities.
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Given :
The focal length of a concave mirror is 18 cm.
To Find :
The radius of curvature of the concave mirror.
Solution :
We know,

Therefore, the radius of curvature of concave mirror is 36 cm.
Hence, this is the required solution.
Sound waves....................................