<prompt> Acha mathbfa anzepmatrix 1 -2 -5 mwishopmatrix, mathbfb anzapmatrix sqrt7 4 -1 mwishopmatrix, na mathbfc anzapmatrix 13 -4 17 mwishopmatrix. Tafuta pembe kati ya vekta mathbfa na mathbfa cdot mathbfc mathbfb - mathbfa cdot mathbfb mathbfc, katika digrii.  <response>: Kumbuka kuwa bidhaa ya nukta mathbfa na mathbfa cdot mathbfc mathbfb - mathbfa cdot mathbfb mathbfc nimathbfa cdot mathbfa cdot mathbfc mathbfb - mathbfa cdot mathbfb mathbfc mathbfa cdot mathbfc mathbfa cdot mathbfb - mathbfa cdot mathbfb mathbfa cdot mathbfc 0.Kwa hivyo, pembe kati ya vekta ni 90circ. 