We'll use the following properties of sine and cosine to prove this:



Then it's just a matter of filling it in...
sin20sin40 * sin60sin80 = 1/2(cos20 - cos60) * 1/2 (cos20 - cos140) =
1/8( cos40 + 1 - cos160 - cos120 - cos40 - cos80 + cos80 + cos200) =
1/8(1 - cos160 - cos120 + cos200) =
1/8(1 - cos160 - cos120 + cos160) =
1/8(1 - cos120 ) = 1/8( 1 + 1/2 ) = 3/16
Answer:
Step-by-step explanation:

Answer:
x = 8.45
Step-by-step explanation:
5.4 + 0.2x = 7.09
Subtract 5.4 from both sides to leave 0.2x alone
0.2x = 1.69
Divide by 0.2 on both sides to isolate x
x = 1.69/0.2
x = 8.45
If width is equal to length then it's a square.
perimeter in this case would be 4x length of each side.
that is( 4 x length)= 210.5
length= width= 210.5/4= 52.62 feet
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