```
f[t_] := -0.024*sqrt[(x'[t])^2 + (y'[t])^2]*(x'[t])
g[t_] := -9.8 - 0.024*sqrt[(x'[t])^2 + (y'[t])^2]*(y'[t])
sol = NDSolve[{x''[t] == f[t], y''[t] == g[t], x'[0] == 11.63,
y'[0] == 8.14, x[0] == y[0] == 0}, {x, y}, {t, 0, 10}]
```

This is supposed to solve for the position of a projectile experiencing quadratic air resistance, but that error is what it keeps returning.