Question

Se senx = 3/5, determine o valor do cosx, sabendo que x pertence ao 1º quadrante

3/4
1
4/5
3/5

Answer 1

$\Large\boxed{\begin{array}{l}\sf sen(x)=\dfrac{3}{5}\implies sen^2(x)=\dfrac{9}{25}\\\sf cos^2(x)=\dfrac{25}{25}-\dfrac{9}{25}=\dfrac{16}{25}\\\\\sf no~1^o~quadrante,cos(x)>0\\\sf portanto\\\sf cos(x)=\sqrt{\dfrac{16}{25}}\\\\\sf cos(x)=\dfrac{4}{5}\end{array}}$