Answer: $1040
A = P + I
A = Total
P = Principal
I = Interest
First find the total amount
A = 640(4)(9)
A = 23040
Plug In the Numbers
23040 = 22000 + I
Substract 22000 on both sides
I = $1040
I assume you're supposed to establish the identity,
cos(A) cos(2A) cos(4A) = 1/8 sin(8A) / sin(A)
Recall the double angle identity for sine:
sin(2<em>x</em>) = 2 sin(<em>x</em>) cos(<em>x</em>)
Then you have
sin(8A) = 2 sin(4A) cos(4A)
sin(8A) = 4 sin(2A) cos(2A) cos(4A)
sin(8A) = 8 sin(A) cos(A) cos(2A) cos(4A)
==> sin(8A)/(8 sin(A)) = cos(A) cos(2A) cos(4A)
as required.
6 2/3 i hope this helped you c:
