If y varies directly as x and y=15 when x =5, what is the value of y when x = 15?
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<span>f(-10)=12, x = -10, y = 12
f(16)=-1, x = 16, y = -1.
so, we have two points, let's check with that,
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</span>![\bf \stackrel{\textit{point-slope form}}{y- y_1= m(x- x_1)} y-12=-\cfrac{1}{2}[x-(-10)] \\\\\\ y-12=-\cfrac{1}{2}(x+10)\implies y-12=-\cfrac{1}{2}x-5\implies y=-\cfrac{1}{2}x+7](https://tex.z-dn.net/?f=%5Cbf%20%5Cstackrel%7B%5Ctextit%7Bpoint-slope%20form%7D%7D%7By-%20y_1%3D%20m%28x-%20x_1%29%7D%20y-12%3D-%5Ccfrac%7B1%7D%7B2%7D%5Bx-%28-10%29%5D%0A%5C%5C%5C%5C%5C%5C%0Ay-12%3D-%5Ccfrac%7B1%7D%7B2%7D%28x%2B10%29%5Cimplies%20y-12%3D-%5Ccfrac%7B1%7D%7B2%7Dx-5%5Cimplies%20y%3D-%5Ccfrac%7B1%7D%7B2%7Dx%2B7)
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f(16)=-1, x = 16, y = -1.
so, we have two points, let's check with that,
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