# Calculating using dv/dt = dh/dt * dv/dh to find dv/dh and then integrating the answer to get a line

#### hardcoremath

##### New member
Hi,
The object the math question is based around for reference is a cylinder
I know
V=pi*r^2*h
dv/dh = pi*r^2

h = 0.00192882t - 1..32( this line was h = -0.00192882t + 1..32 but the question said to multiply the line by -1)
dh/dt= 0.00192882

r = 4

So therefore if I do the rate of change part right right I should get

0.00192882/16pi = dv/dh

then if I integrate I get

h = 0.000378722921381t + c

Is this correct, I have a feeling I did something wrong because I'm not getting the answer I expected.

I expected a line sloping negatively from the 2nd quadrant through the 1st and then to the 4th

#### Dr.Peterson

##### Elite Member
Please state the actual problem you are working on, as requested in our submission guidelines. I have no idea what the line is, or what you are trying to accomplish.

#### HallsofIvy

##### Elite Member
h = 0.00192882t - 1..32( this line was h = -0.00192882t + 1..32
What does "1..32" mean?

#### HallsofIvy

##### Elite Member
"h = 0.00192882t - 1..32( this line was h = -0.00192882t + 1..32 but the question said to multiply the line by -1)". Did you think to wonder WHY? If the first equation is true then the second equation can't be true! You could multiply both sides by -1 so that -h= -0.00192882t+ 1..32. I am still wondering what "1..32" means.