La derivada direccional de F en dirección del vector unitario<img src="https://tex.z-dn.net/?f=%5Cvec%20u" /> se calcula así <img src="https://tex.z-dn.net/?f=D_%7B%5Cvec%20u%7DF%3D%5Cnabla%20F%5Ccdot%20%5Cvec%20u" />
1)<img src="https://tex.z-dn.net/?f=%5Cvec%20u_1%20%3D%20%28%5Ccos%2030%5C%C2%B0%2C%5Csin30%5C%C2%B0%29%3D%5Cleft%28%5Cdfrac%7B%5Csqrt%7B3%7D%7D%7B2%7D%2C%5Cdfrac%7B1%7D%7B2%7D%5Cright%29" />
<img src="https://tex.z-dn.net/?f=D_%7B%5Cvec%20u_1%7DF%3D%5Cnabla%20F%5Ccdot%20%5Cvec%20u_1%5C%5C%20%5C%5C%0AD_%7B%5Cvec%20u_1%7DF%3D%28F_x%2CF_y%29%5Ccdot%20%5Cleft%28%5Cdfrac%7B%5Csqrt%7B3%7D%7D%7B2%7D%2C%5Cdfrac%7B1%7D%7B2%7D%5Cright%29%5C%5C%20%5C%5C%20%5C%5C%0AD_%7B%5Cvec%20u_1%7DF%3D%5Cdfrac%7B%5Csqrt%7B3%7DF_x%7D%7B2%7D%2B%5Cdfrac%7BF_y%7D%7B2%7D%5C%5C%20%5C%5C%20%5C%5C%0AD_%7B%5Cvec%20u_1%7DF%282%2C3%29%3D%5Cdfrac%7B%5Csqrt%7B3%7DF_x%282%2C3%29%7D%7B2%7D%2B%5Cdfrac%7BF_y%282%2C3%29%7D%7B2%7D%5C%5C%20%5C%5C%20%5C%5C%0A%5Cdfrac%7B%5Csqrt%7B3%7DF_x%282%2C3%29%7D%7B2%7D%2B%5Cdfrac%7BF_y%282%2C3%29%7D%7B2%7D%3D2%5C%5C%20%5C%5C%0A%5Csqrt%7B3%7DF_x%282%2C3%29%2BF_y%282%2C3%29%3D4~~~~%5Ccdots%5Ccdots%5Ccdots%5Ctextcircled%7B1%7D%0A" />
2)<img src="https://tex.z-dn.net/?f=%5Cvec%20u_2%3D%28%5Ccos%20150%2C%5Csin%20150%29%3D%5Cleft%28-%5Cdfrac%7B%5Csqrt3%7D%7B2%7D%2C%5Cdfrac%7B1%7D%7B2%7D%5Cright%29%0A" />
<img src="https://tex.z-dn.net/?f=D_%7B%5Cvec%20u_2%7DF%3D%5Cnabla%20F%5Ccdot%20%5Cvec%20u_2%5C%5C%20%5C%5C%0AD_%7B%5Cvec%20u_2%7DF%3D%28F_x%2CF_y%29%5Ccdot%20%5Cleft%28-%5Cdfrac%7B%5Csqrt%7B3%7D%7D%7B2%7D%2C%5Cdfrac%7B1%7D%7B2%7D%5Cright%29%5C%5C%20%5C%5C%20%5C%5C%0AD_%7B%5Cvec%20u_2%7DF%3D-%5Cdfrac%7B%5Csqrt%7B3%7DF_x%7D%7B2%7D%2B%5Cdfrac%7BF_y%7D%7B2%7D%5C%5C%20%5C%5C%20%5C%5C%0AD_%7B%5Cvec%20u_2%7DF%282%2C3%29%3D-%5Cdfrac%7B%5Csqrt%7B3%7DF_x%282%2C3%29%7D%7B2%7D%2B%5Cdfrac%7BF_y%282%2C3%29%7D%7B2%7D%5C%5C%20%5C%5C%20%5C%5C%0A-%5Cdfrac%7B%5Csqrt%7B3%7DF_x%282%2C3%29%7D%7B2%7D%2B%5Cdfrac%7BF_y%282%2C3%29%7D%7B2%7D%3D8%5C%5C%20%5C%5C%0A-%5Csqrt%7B3%7DF_x%282%2C3%29%2BF_y%282%2C3%29%3D16~~~~%5Ccdots%5Ccdots%5Ccdots%5Ctextcircled%7B2%7D%0A" />
(3) resolviendo el sistema
<img src="https://tex.z-dn.net/?f=%5Cbegin%7Bcases%7D%0A%5Csqrt%7B3%7DF_x%282%2C3%29%2BF_y%282%2C3%29%3D4%5C%5C%0A-%5Csqrt%7B3%7DF_x%282%2C3%29%2BF_y%282%2C3%29%3D16%0A%5Cend%7Bcases%7D%5C%5C%20%5C%5C%20%5C%5C%0AF_x%282%2C3%29%3D-2%5Csqrt%7B3%7D%5C%5C%20%0AF_y%282%2C3%29%3D10%5C%5C%20%5C%5C%0A%5Cboxed%7B%5Cnabla%20F%282%2C3%29%3D%5Cleft%28-2%5Csqrt%7B3%7D%2C10%5Cright%29%7D" />
(4) Hallemos el vector tangente a la curva generada por G
<img src="https://tex.z-dn.net/?f=%5Cvec%20v%20%3D%5Cnabla%20G%20%5C%5C%20%5C%5C%0A%5Cvec%20v%20%3D%28G_x%2CG_y%29%5C%5C%20%5C%5C%0A%5Cvec%20v%20%3D%20%282y%2C2x-6y%29%5C%5C%20%5C%5C%0A%5Ctext%7BEn%20el%20punto%20%7D%282%2C1%29%5Ctext%7B%20tenemos%7D%5C%5C%20%5C%5C%0A%5Cvec%20v%3D%282%2C-2%29%5C%5C%20%5C%5C%0A%5Ctext%7BAhora%20el%20vector%20unitario%20de%20%7D%5Cvec%20v%5C%5C%20%5C%5C%0A%5Cvec%20u%3D%5Cleft%28%5Cdfrac%7B1%7D%7B%5Csqrt%7B2%7D%7D%2C-%5Cdfrac%7B1%7D%7B%5Csqrt%7B2%7D%7D%5Cright%29" />
(5) Nos piden calcular<img src="https://tex.z-dn.net/?f=D_%7B%5Cvec%20u%7DF%282%2C3%29%3D%5Cnabla%20F%282%2C3%29%5Ccdot%20%5Cvec%20u" />
<img src="https://tex.z-dn.net/?f=D_%7B%5Cvec%20u%7DF%282%2C3%29%3D%5Cleft%28-2%5Csqrt%7B3%7D%2C10%5Cright%29%5Ccdot%20%5Cleft%28%5Cdfrac%7B1%7D%7B%5Csqrt%7B2%7D%7D%2C-%5Cdfrac%7B1%7D%7B%5Csqrt%7B2%7D%7D%5Cright%29%5C%5C%20%5C%5C%20%5C%5C%0AD_%7B%5Cvec%20u%7DF%282%2C3%29%3D-%5Cdfrac%7B2%5Csqrt%7B3%7D%7D%7B%5Csqrt%7B2%7D%7D-%5Cdfrac%7B10%7D%7B%5Csqrt%7B2%7D%7D%5C%5C%20%5C%5C%20%5C%5C%0A%5Cboxed%7BD_%7B%5Cvec%20u%7DF%282%2C3%29%3D-%5Cdfrac%7B2%5Csqrt%7B3%7D%2B10%7D%7B%5Csqrt%7B2%7D%7D%7D" />.