Aladder 39 feet long leans against a building and reaches the ledge of a window. if the foot of the ladder is 15 feet from the foot of the building, how high is the window ledge about the ground?

First you need to use the Pythagorean theorem (a²+b²=c²).  Let's use 39 feet as a and 15 as b.  c is the answer.  So we have 39² + 15² =c².  Now find what the ² 's equal.  1521+225=1746.  Now square root 1746.  Which will equal 41.7851648316. I will round it to the nearest whole number.  42.  If you need it rounded to nearest 10th then it will be 41.8.

An = 3 *(an-1) - 1

a1 = 2
a2 = 3* (2) - 1 = 6 - 1 = 5
a3 = 3* (5) - 1 = 15 -1 = 14
a4 = 3* (14) - 1 = 42 -1 = 41
a5 = 3* (41) - 1 = 123 -1 = 122