Question

Найти в градусах сумму а + b.
Если sin(a)=2/√5, cos(b)=1/√10.
Углы a и b принадлежат первой четверти.

Answer 1

$1)Sin\alpha=\frac{2}{\sqrt{5}} \\\\Cos\alpha=\sqrt{1-Sin^{2}\alpha}=\sqrt{1-(\frac{2}{\sqrt{5}})^{2}}=\sqrt{1-\frac{4}{5}}=\frac{1}{\sqrt{5}}\\\\2)Cos\beta=\frac{1}{\sqrt{10}}\\\\Sin\beta=\sqrt{1-Cos^{2}\beta}=\sqrt{1-(\frac{1}{\sqrt{10}})^{2}}=\sqrt{1-\frac{1}{10}}=\sqrt{\frac{9}{10}}=\frac{3}{\sqrt{10}}$

$3)Sin(\alpha +\beta )=Sin\alpha Cos\beta +Sin\beta Cos\alpha =\frac{2}{\sqrt{5}}*\frac{1}{\sqrt{10}}+\frac{3}{\sqrt{10}}*\frac{1}{\sqrt{5}}=\frac{2}{\sqrt{5}*\sqrt{10}}+\frac{3}{\sqrt{5}*\sqrt{10}}=\frac{5}{(\sqrt{5})^{2}*\sqrt{2}}=\frac{1}{\sqrt{2}}$

$Sin(\alpha +\beta )=\frac{1}{\sqrt{2}}\\\\\alpha +\beta=45^{o}\\\\Otvet:\boxed{45^{o} }$