Question

If x varies inversely as y3 - 1 and is equal to 3 when
y = 2, find x when y = 4.
(b) 1/3
(d) 1
(a) 1/4
(c) 1/9​

Answer 1

Answer:

1/3

Step-by-step explanation:

as x is inversely proportional to y

y³-1 = k/x

when y is 2

7 = k/3

k=21

now , take y as 4

63= 21/x

x=1/3

Answer 2

We know $x$ ∝ $y$

$x=ky$

Where $k$ is a constant

Given: $y^3-1$ ∝ $\frac{1}{x}$

$y^3-1=\frac{k}{x}$

$y^3-1=\frac{k}{3}$

Here $y=2$

$(2)^3-1=\frac{k}{3}$

$7=\frac{k}{3}$

$k=21$

Now,

$y^3-1=\frac{k}{x}$

$(4)^3-1=\frac{21}{x}$

$63=\frac{21}{x}$

$x=\frac{21}{x}$

$x=\frac{21}{63}$

$x=\frac{1}{3}$