Question

вычислить : 2)соs(a), tg (a) ctg(a) если sin (a)= -2/5 и П<(а)<3П/2

Answer 1

$cosalpha=sqrt{1-sin^2alpha}=sqrt{1-frac4{25}}=sqrt{frac{21}{25}}=pmfrac{sqrt{21}}5\pi textless alpha textless frac{3pi}2Rightarrowcosalpha textless 0\cosalpha=-frac{sqrt{21}}5\tgalpha=frac{sinalpha}{cosalpha}=left(-frac25right):left(-frac{sqrt{21}}5right)=frac25cdotfrac5{sqrt{21}}=frac2{sqrt{21}}\ctgalpha=frac1{tgalpha}=frac{sqrt{21}}2$

Answer 2

огромное спасибо)