m is inversely proportional to g.

when m=90, g=40

find the value of m when g=m

Guest Nov 9, 2014

#2**+10 **

Have a look at the definition of a inversely propotional relationship.

Hence

$$m = \frac{k}{g} \Leftrightarrow k = mg \Leftrightarrow k = 90 \times 40 = 3600$$

Now if

$$m = g$$

we can write

$$m^2 = k = 3600 \Leftrightarrow m = \sqrt{3600} = 60$$

Therefore

$$m = g = 60$$

(11-11-2014 edit)

or

$$m = g = -60$$

reinout-g
Nov 9, 2014

#1**+10 **

$$\\m=\frac{k}{g}\\

90=\frac{k}{40}\\

90*40=k\\

k=3600\\

so\\

m=\frac{3600}{g}\\

$When g=m$\\

m=\frac{3600}{m}\\

m^2=3600\\

m=\pm 60$$

Melody
Nov 9, 2014

#2**+10 **

Best Answer

Have a look at the definition of a inversely propotional relationship.

Hence

$$m = \frac{k}{g} \Leftrightarrow k = mg \Leftrightarrow k = 90 \times 40 = 3600$$

Now if

$$m = g$$

we can write

$$m^2 = k = 3600 \Leftrightarrow m = \sqrt{3600} = 60$$

Therefore

$$m = g = 60$$

(11-11-2014 edit)

or

$$m = g = -60$$

reinout-g
Nov 9, 2014

#3**0 **

Reinout, can the constant be negative.

I know it is not here but it can be can't it?

Also why can't m=g=-60 ?

Melody
Nov 9, 2014

#5**0 **

Alan or Chris, could you please comment on my question here.

two things are directly proportional if as one gets bigger the other also gets proportionally bigger but the constant can be negative, cant it? So how does that work?

Thanks you

Melody
Nov 10, 2014

#6**+5 **

y is inversely proportional to x just means: y = k/x where k can be positive or negative.

"Proportional to" just refers to the magnitude unless otherwise specified.

.

Alan
Nov 10, 2014

#7**0 **

Thank you Alan. I know that what you are saying is correct

BUT

i find it confusing (misleading) because when teachers talk about directly proportional to they tend to say that as one gets bigger the other gets bigger but if the contant is negative this is not true.

Melody
Nov 10, 2014