ขอบคุณมากๆค่ะ ทำแบบนี้ถูกมั้ยคะ
$\left|U\,\right|-[(\left|A1\,\right|+\left|A2\,\right|+\left|A3\,\right|+\left|A4\,\right|+\left|A5\,\right|)-(\left|A1UA2\,\right|...)+(...)-(...)+(...)]$
$=(ุ6\times5\times4\times3\times2) - [(\binom{5}{1} \times (5\times4\times3\times2))-(\binom{5}{2} \times (4\times3\times2))+(\binom{5}{3} \times (3\times2))-(\binom{5}{4} \times (2))+(\binom{5}{5})]$
$=720-[600-240+60-10+1]=720-411=309$ วิธี
|