Question

If y varies directly as x and y-21 when x
is 7, find x when y = -5.

Answer 1

X=-5/3

Explanation:

Y=KX where k is constant

y=kx

21=7k divide both sides by 7

to get 3

then equate

to get answer

Answer 2

Explanation:

Since, y varies directly as x:

`\therefore \: y = kx..(1) \\ (k = constant \: of \: proportionality) \\ at \: y = 21 \: and \: x = 7 \\ 21 = k * 7 \\ k = (21)/(7) = 3 \\ plugging \: k = 3 \: in \: equation \: (1) \\ y = 3x..(2) \\ plugging \: \: y = - 5 \: in \: (2)\\ - 5 = 3x \\ x = ( - 5)/(3) \\ \: \: \: \: \: \: \huge \red{ \boxed{x = - (5)/(3) }}`