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3 years ago

Y varies directly as x when x= 3 and y =12 find y when x =12

1 answer:

3 0

$\bf \qquad \qquad \textit{direct proportional variation}\\\\
\textit{\underline{y} varies directly with \underline{x}}\qquad \qquad y=kx\impliedby 
\begin{array}{llll}
k=constant\ of\\
\qquad variation
\end{array}\\\\
-------------------------------\\\\
\textit{we know that }
\begin{cases}
x=3\\
y=12
\end{cases}\implies 12=k3\implies \cfrac{12}{3}=k\implies 4=k
\\\\\\
thus\qquad \boxed{y=4x}
\\\\\\
\textit{when x = 12, what is \underline{y}?}\qquad \qquad y=4(12)$

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Answer:

The third choice is the one you want

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The slope is -2. That means that the reciprocal slope is 1/2. Using that slope along with the coordinates x = -1 and y = -2, we first write the line using point-slope form and then solve it for y. Start by filling in the m, the x value and the y value:

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Distributing then gives us:

$y+2=\frac{1}{2}x+\frac{1}{2}$

And finally solving for y (I am going to express the 2 on the left as 4/2 when I move it by subtraction in order to add those fractions):

$y=\frac{1}{2}x+\frac{1}{2}-\frac{4}{2}$

And the final equation in slope-intercept form is:

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