A linguist is studying the Yoruba language. Which factor contributed most to its historical spread across West Africa? a. Its adoption as an ECOWAS official language b. The expansion of the Benin Kingdom c. The influence of European colonial rule

12. Find a standard basis vector for \( R^{3} \) that can be added to the set \( \left\{\mathbf{v}_{1}, \mathbf{v}_{2}\right\} \) to produce a basis for \( R^{3} \). (a) \( \mathbf{v}_{1}=(-1,2,3), \mathbf{v}_{2}=(1,-2,-2) \) (b) \( \mathbf{v}_{1}=(1,-1,0), \mathbf{v}_{2}=(3,1,-2) \)

20. If the expression \( \frac{2 i^{2}-3 i}{1-2 i} \) is written in the form \( a+b i \) where a and \( b \) are real numbers and \( i=\sqrt{-1} \), what is the value of a?

(ix) The equation \( \frac{1}{r r} \frac{\partial}{r}\left(r \frac{\partial u}{r r}\right)=\frac{1}{c^{2}} \frac{\partial^{2} u}{\partial t^{2}} \) is one dimensional wave equation in: (a) Cylindrical coordinate (b) Polar coordinate (c) Spherical coordinate (d) None of these

A historian is exploring the demographic patterns in West Africa's high forest zone. Which historical factor best explains the hig population density in this area? a. Absence of significant slave raids b. Consistent low temperatures c. Frequent and devastating wars d. Lack of fertile soils for agriculture

(b) Show that the relation R on the set \( \mathrm{A}=\{1 \), \( 2,3,4,5\} \) given by \( \mathrm{R}=\{(\mathrm{a}, \mathrm{b}):|\mathrm{a}-\mathrm{b}| \) is even \( \} \) is an equivalence relation.