What is a transition zone and how does it relate to the sahel in africa

The environment of the African Transition Zone is known as the Sahel, a semi-arid region of grasslands created by the collision of the Sahara Desert and central African rain forests. The African Transition Zone stretches over a million square miles, and is over 3500 miles in length.

The transition zone is part of the Earth's mantle, and is located between the lower mantle and upper mantle. The collision in Sahel in Africa is a transition zone occurring hope this helped :-) 

2. x2 + 8x + 12 = 0 to prove: x = -6 or x = -2