Solve for the indicated variable each of the following
1. If y varies inversely as x and y = - 2 when x= -8. Find x when y = 6
2. If m varies inversely as n and m-8 when n = 3 , find m when n = 12
3. If y varies inversely as x and y = 10 when x = 5 find y when x = 15
Answers & Comments
Answer:
1. if y varies inversely as x then there is constant k such as
y = k/x
hence, for y = -2 , when x = -8, then
-2 = k/-8
k = -8 × (-2)
k = 16
for y = 6 we have
6 = 16/x
6x = 16
6x/6 = 16/6
x = 16/6 ÷ 2/2
x = 8/3
check:
6 = 16/8/3
6 = 16 × 3/8
6 = 48/8
6 = 6 ✔️
2. if m varies inversely as n then there is constant k such as
m = k/n
hence, for m = -8 , when n = 3, then
-8 = k/3
k = 3 × (-8)
k = -24
for n = 12 we have
m = -24/12
m = -24/12 ÷ 12/12
m = -2
check:
-2 = -24/12
-2 = -2 ✔️
3. if y varies inversely as x then there is constant k such as
y = k/x
hence, for y = 10, when x = 5, then
10 = k/5
k = 5 × 10
k = 50
for x = 15 we have
y = 50/15
y = 50/15 ÷ 5/5
y = 10/3
check:
10/3 = 50/15
10/3 = 50/15 ÷ 5/5
10/3 = 10/3 ✔️