M is directly proportional to r3
When r = 4, M = 160
a) Work out the value of M when r = 2.

M = 20

Step-by-step explanation:

Given that M is directly proportional to r³ then the equation relating them is

M = kr³ ← k is the constant of proportion

To find k use the condition when r = 4, M = 160, that is

160 = k × 4³ = 64k (divide both sides by 64 )

2.5 = k

M = 2.5r³ ← equation of proportion

When r = 2, then

M = 2.5 × 2³ = 2.5 × 8 = 20

because they could drop even lower..

a.

step-by-step explanation:

step 1 distribute 2 to every term in the parentheses

step 2 add 10 on both sides of the equal sign