sin alpha + cos alpha =5/4 tính B= sin alpha×cos alpha 30/08/2021 Bởi Alaia sin alpha + cos alpha =5/4 tính B= sin alpha×cos alpha
$\sin a+\cos a=\dfrac{5}{4}$ $\Leftrightarrow \sin^2a +2\sin a.\cos a+\cos^2a=\dfrac{25}{16}$ $\Leftrightarrow 2B=\dfrac{25}{16}-1=\dfrac{9}{16}$ $\Leftrightarrow B=\dfrac{9}{32}$ Bình luận
Ta có $(\sin \alpha + \cos \alpha)^2 = \sin^2\alpha + \cos^2\alpha + 2\sin \alpha . \cos \alpha$ $<-> \left( \dfrac{5}{4} \right)^2 = 1 + 2B$ $<-> 2B = \dfrac{9}{16}$ $<-> B = \dfrac{9}{32}$ Vậy $B = \dfrac{9}{32}$. Bình luận
$\sin a+\cos a=\dfrac{5}{4}$
$\Leftrightarrow \sin^2a +2\sin a.\cos a+\cos^2a=\dfrac{25}{16}$
$\Leftrightarrow 2B=\dfrac{25}{16}-1=\dfrac{9}{16}$
$\Leftrightarrow B=\dfrac{9}{32}$
Ta có
$(\sin \alpha + \cos \alpha)^2 = \sin^2\alpha + \cos^2\alpha + 2\sin \alpha . \cos \alpha$
$<-> \left( \dfrac{5}{4} \right)^2 = 1 + 2B$
$<-> 2B = \dfrac{9}{16}$
$<-> B = \dfrac{9}{32}$
Vậy $B = \dfrac{9}{32}$.