What does a contour line show?
a. the altitude of a landform
b. the distance around a landform
c. the depth of a landform
d. the north/south layout of a landform

The answer is    (d) 7/2======we have    we also  have an integral      notice how function f splits up at x = 0. there's a left piece and a right pieceso we'll need to do the same thing with our integral: split it at x = 0we use a property of integrals that allows us to split up and sum:     notice that for the piecewise function f, the function has the equationf(x) = x when x  ≤ 0. so for the integral  , f(x) = x so it changes into      for the piecewise function f, the function has the equationf(x) = x+1  when x  > 0. for the integral  , we have    therefore, back to our splitted integral:    

This is called visual imagery. it is a memorization technique wherein an idea or a term is associated with an image, this in remembering ideas, especially as humans are very visual learners. this is also why visual aids a lot for memory retention.