How do I find the exact answer to these questions Without ro

How do I find the exact answer to these questions? Without rounding until the final answer and 3 decimal places.

applying law of cosines to find the planes speed relative to ground

v^2 = 650^2 + 40^2 - 2 (650) (40) cos (135)

v^2 = 424100 + 36769.55

v = 678.87 km / hr

40^2 = 650^2 + 678.87^2 - 2 * 650 * 678.87 cos theta

finding theta

1600 = 883364.4769 - 882531 cos theta

theta = 2.3881

the plane will be off course by 2 degrees 23 minutes 17 seconds