Question

[Herimone]

a, bt sin α=3/5, tính A= 5 \(sin^2\)α + 6\(cos^2\)α.

b,bt cos α= 4/5, tính B= 4\(sin^2\)α - 5\(cos^2\)α.

Answer 1

[Nguyễn Lê Phước Thịnh]

a) Ta có: \(\sin^2\alpha+\cos^2\alpha=1\)

\(\Leftrightarrow\cos^2\alpha=1-\dfrac{9}{25}=\dfrac{16}{25}\)

Ta có: \(A=5\cdot\sin^2\alpha+6\cdot\cos^2\alpha\)

\(=5\left(\sin^2\alpha+\cos^2\alpha\right)+\cos^2\alpha\)

\(=5+\dfrac{16}{25}=\dfrac{141}{25}\)

Answer 2

[Herimone]

phần b ?