Question 751757
Given cosA = -1/4 and 90 degrees < A < 180 degrees, find tanA in surd form
sec(A)=1/cos(A)=-4
{{{tan(A)=-sqrt(sec^2(A)-1)=-sqrt(16-1)=-sqrt(15)}}} (in Q2 where tan<0)
..
Check with calculator:
cos(A)=-1/4
A&#8776;104.4775º
tan(A)=tan(104.4775º)&#8776;-3.873..
Exact value=-&#8730;15&#8776;-3.873..