if the value of y varies directly with x and y= -1 when x=3, find y if x=9

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if the value of y varies directly with x and y= -1 when x=3, find y if x=9

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    2021-10-16T18:51:25+00:00

    y = – 3

    Since y varies directly as x then

    y = kx ← ( k is the constant of variation )

    to find k use y = – 1 when x = 3

    k = \frac{y}{x} = \frac{-1}{3} = – \frac{1}{3}

    hence y = – \frac{1}{3} x

    when x = 9, then

    y = – \frac{1}{3} × 9 = – 3

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