If a is the second quadrant angle and Tan (a - π / 4) = 7, what is sin (a + π / 4) equal to

If a is the second quadrant angle and Tan (a - π / 4) = 7, what is sin (a + π / 4) equal to

tan(a-pi/4)=7
(tana-tanpi/4)/(1+tana*tanpi/4)=7
(tana-1)/(1+tana)=7
tana-1=7+7tana
6tana=-8
tana=-4/3
sina/cosa=-4/3
-4cosa=3sina
If a is the second quadrant angle, then cosa