An airplane is heading due south at a speed of 600 km h. if a wind begins blowing from the
southwest at a speed of 100 km h (average), calculate: (a) the velocity (magnitude and direction) of the plane relative to the ground

Here's what I got:
Let's assume that N and E are + directions while S and W are - directions.
Wind is blowing from SW; thus, it is blowing towards NE (or at 45 deg N of E).
Dividing the wind's speed into components:y-component: +70.71 km/h; x-component: +70.71 km/h
Dividing the airplane's speed into components:y-component: -600 km/h; x-component: 0 km/h
Adding the components to get the resulting components:y-component: -529.29 km/h; x-component: +70.71
Using the Pythagorean Theorem to find the resulting speed:v^2 = y^2 + x^2 so v = 533.99 km/h
To find the angle of direction, use arctan (y/x):arctan (529.29/70.71) = 82.39 deg
ANSWER: velocity = 533.99 km/h at 82.39 deg S of E