Question #d989d

2 Answers
Jan 3, 2018

#cosA=8/17#

Explanation:

#"using the "color(blue)"trigonometric identity"#

#•color(white)(x)sin^2x+cos^2x=1#

#rArrcosx=+-sqrt(1-sin^2x)#

#"since "cotA>0" and "sinA>0#

#"then A is in the first quadrant where cos is positive"#

#cosA=sqrt(1-(15/17)^2)#

#color(white)(cosA)=sqrt(1-225/289)=sqrt(64/289)=8/17#

Jan 4, 2018

#cos(A) = 8/17#

Explanation:

With #cot(A) = cos(A)/sin(A)# we can rearrange:

#cos(A) = cot(A)*sin(A)#

Now we can substitute:

#cos(A) = (8/15)*(15/17) = 8/17#