Step-by-step explanation:
[tex] {sin}^{2} A + {cos}^{2} A = 1 \\ lhs = {sin}^{2} A + {cos}^{2} A \\ = {sin}^{2} A + 1 - {sin}^{2} A \\ = 1 \\ = rhs \\ \therefore \: {sin}^{2} A + {cos}^{2} A = 1 \\ [/tex]
