Answer:
71.6 degrees
Explanation:
The formula for calculating the angle between two vectors is expressed as;
u.v = |u||v|cos theta
u.v = (8, 4).(9, -9)
u.v = 8(9)+4(-9)
u.v = 72-36
u.v = 36
|u| = √8²+4²
|u| = √64+16
|u| = √80
|v| = √9²+(-9)²
|v| = √81+81
|v| = √162
36 = √80*√162 cos theta
36 = √12960 cos theta
36 = 113.84 cos theta
cos theta = 36/113.84
cos theta = 36/113.84
cos theta = 0.3162
theta = arccos (0.3162)
theta = 71.6 degrees
Hence the angle between the given vectors is 71.6 degrees