Mathematics question

[Thinzar]

Can someone explain this to me? The answer is E

[Juliette]

hi
using the trigonometry table:

A) (square root 2)/2 + (square root 2)/2 = square root 2
B) 1 + 0 = 1
C) 1 + 0 = 1
D) 0 + 1 = 1
E) -(square root 2)/2 + (square root 2)/2 = 0
with cos(3pi/4) in the second quadrant so it takes a negative value