Question 881667
<b>1.</b>   Quadrant 3.
{{{cos(theta)=-2/5}}}, but if tangent is positive, the angle must be quadrant 3.  This means also that {{{sin(theta)<0}}}.
Letting y=sine,  
{{{(-2/5)^2+y^2=1}}}
{{{y^2=1-4/25}}}
{{{y=-sqrt((25-4)/25)}}}
{{{highlight(y=-sqrt(21)/5)}}}


<b>3.</b>   Quadrant 4.  Cosine is positive.
Radius is {{{sqrt(25+144)=sqrt(169)=13}}}.
{{{highlight(cos(theta)=5/13)}}}