2. จงหาผลคูณ
1) \(\mathsf{(-\frac{2}{3}) \times \frac{4}{3} \times \frac{6}{8}}\)
วิธีทำ
\(\mathsf{(-\frac{2}{3}) \times \frac{4}{3} \times \frac{6}{8}}\) = \(\mathsf{(-\frac{2}{3}) \times \frac{4^1\mkern-14mu\color{Red}/}{3_1\mkern-15mu\color{Red}/} \times \frac{6^2\mkern-15mu\color{Red}/}{8_2\mkern-15mu\color{Red}/}}\)
= \(\mathsf{(-\frac{2}{3}) \times \frac{1}{1} \times \frac{2}{2}}\)
= \(\mathsf{(-\frac{2}{3}) \times 1 \times 1}\)
= \(\mathsf{-\frac{2}{3}}\)
ตอบ \(\mathsf{-\frac{2}{3}}\)
2) \(\mathsf{(-\frac{1}{7}) \times (-\frac{7}{4}) \times \frac{16}{3}}\)
วิธีทำ
\(\mathsf{(-\frac{1}{7}) \times (-\frac{7}{4}) \times \frac{16}{3}}\) = \(\mathsf{(-\frac{1}{7_1\mkern-17mu\color{Red}/}) \times (-\frac{7^1\mkern-17mu\color{Red}/}{4_1\mkern-15mu\color{magenta}/}) \times \frac{16^4\mkern-18mu\color{magenta}/}{3}}\)
= \(\mathsf{(-\frac{1}{1}) \times (-\frac{1}{1}) \times \frac{4}{3}}\)
= \(\mathsf{(-1) \times (-1) \times \frac{4}{3}}\)
= \(\mathsf{\frac{4}{3}}\)
= \(\mathsf{1\frac{1}{3}}\)
ตอบ \(\mathsf{1\frac{1}{3}}\)
3) \(\mathsf{\frac{3}{5} \times (-\frac{5}{3}) \times \frac{12}{15}}\)
วิธีทำ
\(\mathsf{\frac{3}{5} \times (-\frac{5}{3}) \times \frac{12}{15}}\) = \(\mathsf{\frac{3^1\mkern-15mu\color{Red}/}{5_1\mkern-15mu\color{Red}/} \times (-\frac{5^1\mkern-15mu\color{Red}/}{3_1\mkern-15mu\color{Red}/}) \times \frac{12^4\mkern-18mu\color{magenta}/}{15_5\mkern-18mu\color{magenta}/}}\)
= \(\mathsf{\frac{1}{1} \times (-\frac{1}{1}) \times \frac{4}{5}}\)
= \(\mathsf{1 \times (-1) \times \frac{4}{5}}\)
= \(\mathsf{-\frac{4}{5}}\)
ตอบ \(\mathsf{-\frac{4}{5}}\)
4) \(\mathsf{(-\frac{3}{7})(-\frac{4}{5})(-\frac{7}{12})}\)
วิธีทำ
\(\mathsf{(-\frac{3}{7})(-\frac{4}{5})(-\frac{7}{12})}\) = \(\mathsf{(-\frac{3^1\mkern-15mu\color{magenta}/}{7_1\mkern-17mu\color{Red}/})(-\frac{4}{5})(-\frac{7^1\mkern-17mu\color{Red}/}{12_4\mkern-18mu\color{magenta}/})}\)
= \(\mathsf{(-\frac{1}{1})(-\frac{4}{5})(-\frac{1}{4})}\)
= \(\mathsf{(-1)(-\frac{4^1\mkern-15mu\color{Red}/}{5})(-\frac{1}{4_1\mkern-14mu\color{Red}/})}\)
= \(\mathsf{(-1)(-\frac{1}{5})(-\frac{1}{1})}\)
= \(\mathsf{(-1)(-\frac{1}{5})(-1)}\)
= \(\mathsf{-\frac{1}{5}}\)
ตอบ \(\mathsf{-\frac{1}{5}}\)
5) \(\mathsf{(-5\frac{1}{4})(-2\frac{1}{2})(-\frac{4}{7})(\frac{2}{15})}\)
วิธีทำ
\(\mathsf{(-5\frac{1}{4})(-2\frac{1}{2})(-\frac{4}{7})(\frac{2}{15})}\) = \(\mathsf{(-\frac{21}{4})(-\frac{5}{2})(-\frac{4}{7})(\frac{2}{15})}\)
= \(\mathsf{(-\frac{21^3\mkern-18mu\color{magenta}/}{4_1\mkern-15mu\color{Lime}/})(-\frac{5^1\mkern-15mu\color{Red}/}{2_1\mkern-15mu\color{Blue}/})(-\frac{4^1\mkern-15mu\color{Lime}/}{7_1\mkern-17mu\color{magenta}/})(\frac{2^1\mkern-15mu\color{Blue}/}{15_3\mkern-18mu\color{Red}/})}\)
= \(\mathsf{(-\frac{3}{1})(-\frac{1}{1})(-\frac{1}{1})(\frac{1}{3})}\)
= \(\mathsf{(-\frac{3^1\mkern-15mu\color{Red}/}{1})(-1)(-1)(\frac{1}{3_1\mkern-15mu\color{Red}/})}\)
= \(\mathsf{(-\frac{1}{1})(\frac{1}{1})}\)
= \(\mathsf{(-1)(1)}\)
= \(\mathsf{-1}\)
ตอบ \(\mathsf{-1}\)
6) \(\mathsf{\frac{23}{4} \times (-\frac{16}{7}) \times \frac{8}{5} \times (-\frac{11}{12}) \times 0}\)
ตอบ 0
7) \(\mathsf{\frac{3}{4} \times (-\frac{7}{10}) \times \frac{4}{3}}\)
วิธีทำ
\(\mathsf{\frac{3}{4} \times (-\frac{7}{10}) \times \frac{4}{3}}\) = \(\mathsf{\frac{3^1\mkern-15mu\color{Red}/}{4_1\mkern-14mu\color{magenta}/} \times (-\frac{7}{10}) \times \frac{4^1\mkern-14mu\color{magenta}/}{3_1\mkern-15mu\color{Red}/}}\)
= \(\mathsf{\frac{1}{1} \times (-\frac{7}{10}) \times \frac{1}{1}}\)
= \(\mathsf{1 \times (-\frac{7}{10}) \times 1}\)
= \(\mathsf{-\frac{7}{10}}\)
ตอบ \(\mathsf{-\frac{7}{10}}\)
8) \(\mathsf{(-\frac{1}{6}) \times \frac{2}{5} \times (-6)}\)
วิธีทำ
\(\mathsf{(-\frac{1}{6}) \times \frac{2}{5} \times (-6)}\) = \(\mathsf{(-\frac{1}{6_1\mkern-15mu\color{Red}/}) \times \frac{2}{5} \times (-6^1\mkern-18mu\color{Red}/\;)}\)
= \(\mathsf{(-\frac{1}{1}) \times \frac{2}{5} \times (-1)}\)
= \(\mathsf{(-1) \times \frac{2}{5} \times (-1)}\)
= \(\mathsf{\frac{2}{5}}\)
ตอบ \(\mathsf{\frac{2}{5}}\)