[กิตติ]

ข้อ 11 ตอนที่2
$\frac{a}{2-a} =\frac{b}{7-b}=\frac{c}{15-c} $
$\frac{2-a}{a} =\frac{7-b}{b}=\frac{15-c}{c} $
$\frac{2}{a} =\frac{7}{b}=\frac{15}{c} $
$\frac{a}{2} =\frac{b}{7}=\frac{c}{15}=k$......(1)
$\frac{a+b+c}{2+7+15}=\frac{a+b+c}{24} =k $
$\frac{-a}{-2} =\frac{-b}{-7}=\frac{c}{15}=k$
$\frac{c-b-a}{15-7-2}=\frac{c-b-a}{6}=k $....(2)
(1)=(2) $\frac{c-b-a}{6}=\frac{a+b+c}{24}=k$
$c-b-a=\frac{16\times 6}{24} =4$