Ответ:

  1. \(4b^2-9=(2b-3)(2b+3)\), \(9b+9a=9(a+b)\).

    \[\frac{3-2b}{a+b}\cdot\frac{9(a+b)}{(2b-3)(2b+3)}-\frac{6b}{2b+3}=-\frac9{2b+3}-\frac{6b}{2b+3}=-\frac{3(2b+3)}{2b+3}=-3.\]

    Жауабы: \(-3\).

  2. \(16a^2-25c^2=(4a-5c)(4a+5c)\), \(ac+c^2=c(a+c)\).

    \[\frac{(4a-5c)(4a+5c)}{c(a+c)}\cdot\frac{3c}{5c-4a}+\frac{3(7a+8c)}{a+c}\]

    Since \(5c-4a=-(4a-5c)\), the first term is \(-\frac{3(4a+5c)}{a+c}\). Therefore

    \[\frac{-12a-15c+21a+24c}{a+c}=\frac{9a+9c}{a+c}=9.\]

    Жауабы: \(9\).

  3. \(b^3+27=(b+3)(b^2-3b+9)\), \(2b^2-6b+18=2(b^2-3b+9)\).

    \[\frac{b+2}{b^2-3b+9}-\frac6{(b+3)(b^2-3b+9)}=\frac{(b+2)(b+3)-6}{(b+3)(b^2-3b+9)}=\frac{b(b+5)}{(b+3)(b^2-3b+9)}.\]

    Деление на \(\frac{3(b+5)}{2(b^2-3b+9)}\):

    \[\frac{b(b+5)}{(b+3)(b^2-3b+9)}\cdot\frac{2(b^2-3b+9)}{3(b+5)}=\frac{2b}{3(b+3)}.\]

    Жауабы: \(\frac{2b}{3(b+3)}\).

  4. \(a^3-8=(a-2)(a^2+2a+4)\).

    \[\frac{a-1}{a^2+2a+4}-\frac2{(a-2)(a^2+2a+4)}=\frac{(a-1)(a-2)-2}{(a-2)(a^2+2a+4)}=\frac{a(a-3)}{(a-2)(a^2+2a+4)}.\]

    Деление на \(\frac{3-a}{a^2+2a+4}=-\frac{a-3}{a^2+2a+4}\):

    \[\frac{a(a-3)}{(a-2)(a^2+2a+4)}\cdot\frac{a^2+2a+4}{3-a}=-\frac{a}{a-2}.\]

    Жауабы: \(-\frac{a}{a-2}\).

  5. \[\frac{a}{a+8}+\frac{a}{7-a}=\frac{a(7-a)+a(a+8)}{(a+8)(7-a)}=\frac{15a}{(a+8)(7-a)}.\]

    Сонда

    \[\frac{15a}{(a+8)(7-a)}:\frac{a}{a+8}=\frac{15}{7-a}.\]

    \[\frac{2a+1}{a-7}+\frac{15}{7-a}=\frac{2a+1}{a-7}-\frac{15}{a-7}=\frac{2a-14}{a-7}=2.\]

    Жауабы: \(2\).

  6. \[\frac{b}{2b-3}-\frac{b}{2b+3}=\frac{6b}{(2b-3)(2b+3)}=\frac{6b}{4b^2-9}.\]

    \(9+12b+4b^2=(2b+3)^2\), сондықтан

    \[\frac{6b}{(2b-3)(2b+3)}:\frac{b}{(2b+3)^2}=\frac{6(2b+3)}{2b-3}.\]

    Ал \(\frac{45-6b}{3-2b}=\frac{6b-45}{2b-3}\). Демек,

    \[\frac{6(2b+3)+6b-45}{2b-3}=\frac{18b-27}{2b-3}=9.\]

    Жауабы: \(9\).

  7. \(\sqrt{4b}=2\sqrt b\), \(\sqrt{0.16b}=0.4\sqrt b\).

    \[25\sqrt b-0.5\cdot2\sqrt b+100\cdot0.4\sqrt b=(25-1+40)\sqrt b=64\sqrt b.\]

    Жауабы: \(64\sqrt b\).