Direct variation usually conform to the general formula : [tex]y = kx [/tex] where k is the proportionality constant. Hence sorting the equation into tbe appropriate category :
Direct variation :
y = 3x
- Constant of proportionality, k = 3
y = (2/7)x
- Constant of proportionality, k = 2/7
y = -0.5x
- Constant of proportionality, k = -0.5
Non - direct variation :
y = 2.2x + 7
- Linear equation expressed in slope - intercept form
y = 4 and x = - 1
- These are variable declarations as the constants are only assigned to one variable and no unknown.
Therefore, only three of the expressions exhibit direct variation while the other three do not.
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