First we calculate how many ways you can choose four books from a set of eight.
We use the formula n! / [r! * (n-r)!]
8! / [4! * 4!]
= 8*7*6*5 / 4*3*2*1 = 70 ways
Then we have to calculate how many permutations can be made from 4 objects which equals 4*3*2*1 = 24
So, the TOTAL number of ways = 70 * 24 = 1,680
what do you have to do???
Answer:
DC = 10.93 cm , AC = 9.8 cm
Step-by-step explanation:
From trigonometry;
⇒ Tan 60 = AB/BD
⇒AB = BD Tan 60 ( where BD = 4 cm )
⇒ AB = 6.93 cm
Also, AB=BC , therefore;
⇒ BC = 6.93 cm
⇒ Cos 60 = BD/AD
⇒ AD = BD/ Cos 60 = 4/Cos 60
⇒ AD = 8 cm
From Pythagoras theorem;
⇒
=
+
=
+ 
⇒ AC =
= 9.80 cm
⇒ DC = BD + BC = 4 + 6.93
⇒ DC = 10.93 cm