Question

bieets \(cosa=\frac{1}{3}\)khi đó \(A=3sin^2a+cos^2a\) là .......... (giải thích rõ ràng )

Answer 1

\(A=3\sin^2\alpha+3\cos^2\alpha-2\cos^2\alpha\)

    \(=3\left(\sin^2\alpha+\cos^2\alpha\right)-2\cos^2\alpha=3.1-2.\left(\frac{1}{3}\right)^2=\frac{25}{9}\)

Answer 2

Ta có

\(sin^2a+cos^2a=1\)

<=>\(sin^2a=1-cos^2a=1-\frac{1}{9}=\frac{8}{9}\)

=>A=\(3.\frac{8}{9}+\frac{1}{9}=\frac{25}{9}\)

Tick nha