When you want to know the amount of fencing needed, you have to find the perimeter of the enclosed space. For the shape of a rectangle, the perimeter is the sum of its sides. Its sides consist of 2 equal lengths and 2 equal widths. Therefore:
A = 2L + 2W = 18(2) + 45(2) = 126 feet
It will need 126 feet of fencing.
Notice that
• <em>π</em>/2 = <em>π</em>/3 + <em>π</em>/6
• <em>π</em>/6 = <em>π</em>/3 - <em>π</em>/6
Recall the angle sum identities for sine:
sin(<em>x</em> + <em>y</em>) = sin(<em>x</em>) cos(<em>y</em>) + cos(<em>x</em>) sin(<em>y</em>)
sin(<em>x</em> - <em>y</em>) = sin(<em>x</em>) cos(<em>y</em>) - cos(<em>x</em>) sin(<em>y</em>)
By adding these together, we get
sin(<em>x</em> + <em>y</em>) + sin(<em>x</em> - <em>y</em>) = 2 sin(<em>x</em>) cos(<em>y</em>)
==> sin(<em>x</em>) cos(<em>y</em>) = 1/2 (sin(<em>x</em> + <em>y</em>) + sin(<em>x</em> - <em>y</em>))
Now take <em>x</em> = <em>π</em>/3 and <em>y</em> = <em>π</em>/6 :
sin(<em>π</em>/3) cos(<em>π</em>/6) = 1/2 (sin(<em>π</em>/2) + sin(<em>π</em>/6))
So the blank should be filled with cos.
Answer:
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