# Rates of change: The rate of change of the area of a triangle. Is my answer right?

my question is... is this answer correct? for the last step. WOULDNT you multiply 10x by .5 and 12 by .2? the opposite of what this answer is? Itsays BASE is 10 in and BASE chagnges at .5 in per second
problem:
i45.tinypic.com/xknbci.png
i50.tinypic.com/2qcnsyv.jpg

this is what i get...

i50.tinypic.com/124cxgy.jpg

## Answers and Replies

SammyS
Staff Emeritus
Homework Helper
Gold Member

my question is... is this answer correct? for the last step. WOULDN'T you multiply 10[STRIKE]x[/STRIKE] by .5 and 12 by .2? the opposite of what this answer is? It says BASE is 10 in and BASE changes at .5 in per second
problem:
i45.tinypic.com/xknbci.png
i50.tinypic.com/2qcnsyv.jpg

this is what i get...

i50.tinypic.com/124cxgy.jpg
Hello indigo1. Welcome to PF !

Why would you want to multiply the base by the rate of change of the base? Even your working has $\displaystyle b\frac{dh}{dt}$ and $\displaystyle h\frac{db}{dt}\ .$

dh/dt is -0.2 in/sec and db/dt is 0.5 in/sec !

BTW: Below are your images, displayed so others can see them.

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This was really helpful
But i was wondering if this is the same for my HW problem i applied the same A' equation but instead looked for the db/dt and i got -3/2 idk if this is right.
"The base of an isosceles triangle is 6 feet. If the altitude is 4 feet and increasing at the rate of 2 inches per minute, at what rate is the vertex angle changing?"
I will really appreciate for your help.

Mark44
Mentor
seawolf23, instead of tacking your question onto the end of a question from almost two years ago, please start a new thread. Be sure to use the homework template, and include the problem statement and the work you have done.