<span>Part I </span> <span>The double angle identity for sine states that sin(2x) = 2sinxcosx </span> <span>Thus we get: </span> <span>sin(2x) - sin(2x)cos(2x) = 0 </span>
<span>Part II </span> <span>sin(2x)(1 - cos(2x)) = 0 </span>
<span>Part III </span> <span>Either sin(2x) = 0 or </span> <span>1 - cos(2x) = 0 </span> <span>=> cos(2x) = 1 </span>
<span>For sin(2x) = 0, this is true for </span> <span>2x = n(pi) where n = 0, 1, 2, .... </span> <span>x = n(pi/2) </span>
<span>For cos(2x) = 1, this is true for </span> <span>2x = n(pi) where n = 0, 2, 4, .... </span> <span>x = n(pi/2) </span>
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First, find the percentage of 23.50 (equation in the parenthesis). 18% is equivalent to 0.18. Then, you add that to 23.50. That's the total amount Sam should pay. I hope this makes sense.