Bài 9:
a) x và y là hai đại lượng tỉ lệ thuận theo hệ số k nên:
\(\dfrac{y}{x}=k\Rightarrow k=\dfrac{\dfrac{8}{15}}{\dfrac{2}{3}}=\dfrac{4}{5}\)
b) Ta có:
\(\dfrac{y}{x}=k\Rightarrow y=kx=\dfrac{4}{5}x\)
Ta có:
\(\dfrac{y}{x}=k\Rightarrow x=\dfrac{y}{k}=\dfrac{y}{\dfrac{4}{5}}=\dfrac{5}{4}y\)
c) Khi:
\(x=1\Rightarrow y=\dfrac{4}{5}\cdot1=\dfrac{4}{5}\)
\(x=-2\Rightarrow y=\dfrac{4}{5}\cdot-2=\dfrac{-8}{5}\)
\(x=5\Rightarrow y=\dfrac{4}{5}\cdot5=4\)
\(x=\dfrac{2}{3}\Rightarrow y=\dfrac{4}{5}\cdot\dfrac{2}{3}=\dfrac{8}{15}\)
\(x=\dfrac{-5}{4}\Rightarrow y=\dfrac{4}{5}\cdot\dfrac{-5}{4}=-1\)
d) Khi:
\(y=3\Rightarrow x=\dfrac{5}{4}\cdot3=\dfrac{15}{4}\)
\(y=-4\Rightarrow x=\dfrac{5}{4}\cdot-4=-5\)
\(y=-5\Rightarrow x=\dfrac{5}{4}\cdot-5=-\dfrac{25}{4}\)
\(y=\dfrac{6}{5}\Rightarrow x=\dfrac{5}{4}\cdot\dfrac{6}{5}=\dfrac{3}{2}\)
\(y=-\dfrac{3}{4}\Rightarrow x=\dfrac{5}{4}\cdot\dfrac{-3}{4}=\dfrac{-15}{16}\)
