Tính B= cos^2 25 + cos^2 35 + cos^2 45 + cos^2 55 + cos^2 65. giúp mình nha 10/07/2021 Bởi Reese Tính B= cos^2 25 + cos^2 35 + cos^2 45 + cos^2 55 + cos^2 65. giúp mình nha
$\cos^225^o+\cos^235^o+\cos^245^o+\cos^255^o+\cos^265^o$ $=\cos^225^o+\cos^235^o+\cos^245^o+\sin^235^o+\sin^225^o$ $=1+1+(\dfrac{\sqrt2}{2})^2$ $=\dfrac{5}{2}$ Bình luận
Đáp án:
$\cos^225^o+\cos^235^o+\cos^245^o+\cos^255^o+\cos^265^o$
$=\cos^225^o+\cos^235^o+\cos^245^o+\sin^235^o+\sin^225^o$
$=1+1+(\dfrac{\sqrt2}{2})^2$
$=\dfrac{5}{2}$