Direct variation

Question

Suppose that y varies directly with as x and y=-9 when x=3 Find the value of x when y=18

Answer 1

y varies directly as x can be expressed as:

y = kx, where k is the constant of variation

y = -9 when x = 3, so can plug those into determine k:

-9 = k*3 so k = -3

so can now expression relationship as

y= -3x

To find value of x when y = 18, plug 18 in for value of y and solve for x:

18 = -3x

x = -6