B=am-an+bm-bn
B=a(m-n)+b(m-n)
=> B=a.27+b.27
B=27(a+b)
=> B=27.9
B=243
\(B=am-an+bm-bn=a\left(m-n\right)+b\left(m-n\right)=\left(a+b\right)\left(m-n\right)=9.27=243\)
B = am - an + bm - bn
B = a(m-n) + b(m-n)
B = (a+b) (m-n)
thay số vào ta có:
B = (a+b) (m-n)
B = 9 * 27
B =243