f(7) = p.77 + q.73 + r.7 - 4 = -p.(-7)7 - q.(-7)3 - r.(-7) - 4
= -[p.(-7)7 + q.(-7)3 + r.(-7)] - 4 = -[f(-7) + 4] - 4
= -(3 + 4) - 4 = -7 - 4 = -11
2
