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.
∆volume = 4/3 *pi * (R^3 -r^3 )
= 4/3 *pi*((6)^3 -(3)^3)
= 252*pi
= 791.68 m^3
Answer: 1 gallon costs 0.40 $
Step-by-step explanation: 6 gallons / 15$ = 0.4 gal/$
$400.72 - This is how it’s done.
