Question 1138139
You want sine of some alpha angle.

Draw right triangle
legs y and 3; hypotenuse 5;
alpha is  opposite of y.


{{{y^2+3^2=5^2}}}  for {{{cos(alpha)=3/5}}};
{{{y=sqrt(5^2-3^2)}}}

{{{sin(alpha)=sqrt(5^2-3^2)/5}}}


{{{highlight(4/5)}}}