Question

Cho: (a + 3).(b - 4) - (a - 3).( b + 4)= 0

Chứng minh: \(\dfrac{a}{3}\) = \(\dfrac{b}{4}\)

Answer 1

\(\left(a+3\right)\left(b-4\right)-\left(a-3\right)\left(b+4\right)=0\\ \Leftrightarrow ab-4a+3b-12-\left(ab+4a-3b-12\right)=0\\ \Leftrightarrow ab-4a+3b-12-ab-4a+3b+12=0\\\Leftrightarrow6b-8a=0\\ \Leftrightarrow6b=8a\\ \Leftrightarrow3b=4a\\ \Leftrightarrow \dfrac{a}{3}=\dfrac{b}{4}\)