Đáp án:
`7)`
`16b^4-9c^2`
`=(4b^2)^2-(3c)^2`
`=(4b^2 +3c).(4b^2-3c)`
`8)`
`81a^2 b^2 -9x^2`
`=9.(9a^2b^2-x^2)`
`=9.[(3ab)^2-x^2]`
`=9.(3ab+x).(3ab-x)`
`9)`
`x^4 y^3 -yz^2`
`=y(x^4 y^2 -z^2)`
`=y.[(x^2 y)^2-z^2]`
`=y.(x^2 y-z).(x^2 y+z)`
`10)`
`a^6-4`
`=(a^3)^2-2^2`
`=(a^3-2).(a^3+2)`
`11)`
`(a+3y)^2-z^2`
`=(a+3y-z).(a+3y+z)`
`12)`
`(5p+3q)^2-25`
`=(5p+3q)^2-5^2`
`=(5p+3q-5).(5p+3q+5)`
`13)`
`y^2-1/4`
`=y^2-(1/2)^2`
`=(y-1/2).(y+1/2)`
`14)`
`(a-b)^2-1`
`=(a-b)^2-1^2`
`=(a-b-1).(a-b+1)`
`15)`
`p^2-(q-r)^2`
`=[p-(q-r)].[p+(q-r)]`
`=(p-q+r).(p+q-r)`
`16)`
`a^2 b -b^3 (x+y)^2`
`=b[a^2-b^2 . (x+y)^2]`
`=b.[a^2-(bx+by)^2]`
`=b[a-(bx+by)].[a+(bx+by)]`
`=b(a-bx-by).(a+bx+by)`
`17)`
`6a^2-(x+y)^2`
`=(a\sqrt{6})^2-(x+y)^2`
`=[a\sqrt{6}-(x+y)].[a\sqrt{6}+(x+y)]`
`=(a\sqrt{6}-x-y).(a\sqrt{6}+x+y)`
`18)`
`1-(x-y)^2`
`=1^2-(x-y)^2`
`=[1-(x-y)].[1+(x+y)]`
`=(1-x+y).(1+x+y)`
`19)`
`xy^2-(x-y)^2`
`=(\sqrt{x})^2 . y^2 -(x-y)^2`
`=(y\sqrt{x})^2-(x-y)^2`
`=[y\sqrt{x}-(x-y)].[y\sqrt{x}+(x-y)]`
`=(y\sqrt{x}-x+y).(y\sqrt{x}+x-y)`
`20)`
`(4+7a)^2-(8-9c)^2`
`=[(4+7a)-(8-9c)].[(4+7a)+(8-9c)]`
`=(4+7a-8+9c).(4+7a+8-9c)`
`=(7a+9c-4).(7a-9c+12)`
`21)`
`4(x+y)^2-z^2`
`=2^2 .(x+y)^2 -z^2`
`=(2x+2y)^2-z^2`
`=(2x+2y-z).(2x+2y+z)`
`23)`
`1/4 (a+b)^2-1`
`=(1/2)^2 . (a+b)^2 -1`
`=(1/2 .a +1/2 . b )^2 -1^2`
`=(1/2 a +1/2 b -1).(1/2 a +1/2 b +1)`
`24)`
`9(a-b)^2-4(x-y)^2`
`=3^2 .(a-b)^2 -2^2 (x-y)^2`
`=(3a-3b)^2 -(2x-2y)^2`
`=[(3a-3b)-(2x-2y)].[(3a-3b)+(2x-2y)]`
`=(3a-3b-2x+2y).(3a-3b+2x-2y)`
