Explaining the capital asset pricing model

Describe the Capital Asset Pricing Model.

Expected return rises linearly with beta. CAPM says $\mathbb{E}[R_i]=r_f+\beta_i(\mathbb{E}[R_m]-r_f)$: only systematic market risk is priced, since idiosyncratic risk can be diversified away. It rests on assumptions such as mean-variance investors, common expectations, and borrowing and lending at the risk-free rate, and is widely used for the cost of equity despite mixed empirical support.