<p>i need some explanation on #18 and #20, section 7, test 8 in the blue book :D please help.</p>
<p>someone with the book please helppppp 
the questions are too complicated to post :(</p>
<h1>18</h1>
<p>Start ABC
Step1 BAC
Step2 BCA
3(repeat s1 and switch the first two letters)=> CBA
4(repeat s2 and switch the last two letters)=> CAB
5 ACB
6 ABC
So the original order ABC reappears at step6(D)</p>
<h1>20</h1>
<p>AR+RC=8
SA=6-AR, CT=6-RC
=> SA+CT=(6-AR)+(6-RC)=12-(AR+RC)=12-8=4</p>
<p>Arc SBT equals (2<em>6</em>π(pi))/4=3*π(pi)</p>
<p>Because ARCB is a rectangle, its diagonals are equal, so AC=RB=6(Radius)</p>
<p>The perimeter of the shaded region equals Arc SBT+(SA+CT)+AC=3<em>π(pi)+4+6=10+3</em>π(B)</p>
<p>Hope that helps.:)</p>
<p>brilliant! i owe you a lot :D</p>