Hãy tính (a) A = sin^2(5 độ) + sin^2(25 độ) + sin^2(45 độ) + sin^2 (65 độ)+ sin^2(85 độ);

a) A = sin²5⁰ + sin²25⁰ + sin²45⁰ + sin²65⁰ + sin²85⁰

A = (sin²5⁰ + sin²85⁰) + (sin²25⁰ + sin²65⁰) + sin²45⁰

A = sin²90⁰ + sin²90⁰ + sin²45⁰

\[A = {\left( 1 \right)^2} + {\left( 1 \right)^2} + {\left( {\frac{{\sqrt 2 }}{2}} \right)^2} = 2 + \frac{1}{2} = \frac{5}{2}\]

b) B = cos²52⁰ sin45⁰ + sin²52⁰cos45⁰;

B = cos²52⁰ sin45⁰ + sin²52⁰ sin45⁰

B = sin45⁰(cos²52⁰ + sin²52⁰)

\[B = \frac{{\sqrt 2 }}{2} \cdot 1 = \frac{{\sqrt 2 }}{2}\]