Consider for a moment building a tree with all possible choices. The first row would contain 8 books (each possible choice for the first book). Then, the second row would contain 7 books for each book in the first row (the choices possible for the second book). Otherwise, it would be 8*7. Following this principal, we continue to multiply down to 1. 8*7*6*5*4*3*2*1. This is also known as 8!, a factorial.
Finally, 8! = 40,320
The first one ,to substitute 3xy from -16 ...so divided both side by 3 .so, (xy =-5.33). the second one,5xy =-20. so,divided both sides by 5 so xy = -4....
a right triangle has one angle that measures 90 degrees. that leaves 90 degrees for the other 2 angles
90 = 40 + other angle
subtract 40 from each side
50 = other angle
Answer = 50 degrees
