Question

Which is equal to the expression below?

(x-3x)+(3x-5x)+(5x-7x)+...+(23x- 25x)

A.
-26x
B.
-24x
C.
24x
D.
26x

Answer 1

-24x. This is an example of a "telescoping series". If you notice, the last and first part of each term cancel out. Take away the parenthesis and you'll see it. x-3x+3x-5x+5x-7x+7x... everything goes away except x-25x so it's -24x.