Rút gọn biểu thức:
a) \(4{a^2}{\cos ^2}{60^2} + 2ab.{\cos ^2}{180^0} + \frac{4}{3}{b^2}{\cos ^2}{30^0}\)
b) \(\left( {a\sin {{90}^0} + b\tan {{45}^0}} \right)\left( {a\cos {0^0} + b\cos {{180}^0}} \right)\)
a) \(4{a^2}{\cos ^2}{60^2} + 2ab.{\cos ^2}{180^0} + \frac{4}{3}{b^2}{\cos ^2}{30^0}\)
\(4{a^2} + \frac{1}{4} + 2a.1 + \frac{4}{3}{b^2}.\frac{3}{4} = {a^2} + 2ab + {b^2} = {\left( {a + b} \right)^2}\)
b) \(\left( {a\sin {{90}^0} + b\tan {{45}^0}} \right)\left( {a\cos {0^0} + b\cos {{180}^0}} \right)\)
\(\left( {a.1 + b.1} \right)\left( {a.1 + b.\left( { - 1} \right)} \right) = \left( {a + b} \right)\left( {a - b} \right) = {a^2} - {b^2}\)
-- Mod Toán 10