Tuesday

September 16, 2014

September 16, 2014

Posted by **Anonymous** on Wednesday, April 4, 2012 at 2:09pm.

I don't know where and how to start.

please help and thank you

- math problem -
**Reiny**, Wednesday, April 4, 2012 at 2:28pmmake a sketch.

Assuming that the gutter is rectangular and the sides must have the same height, look at the cross section of the gutter.

let the base by y and each of the sides by x

we know that

2x + y = 40

y = 40-2x

the area A of the cross-section will be

A = xy

= x(40-2x) = 40x - 2x^2

Assuming this is a typical Calculus question ...

dA/dx = 40 - 4x = 0 for a max of A

40-4x = 0

x = 10

the the depth will be 10 cm

if you don't know Calculus , you will have to complete the square on

A = 40x - 2x^2

- math problem -
**Anonymous**, Wednesday, April 4, 2012 at 2:43pmI don't know calculus

This is what I got after completing the square:

A=-2(x-10)^2+200

How do I know what is the depth when I complete the square?

thank you

**Answer this Question**

**Related Questions**

pre-calc - construction of a rain gutter: a piece of rectangular sheet metal is ...

geometry - a piece of rectangular sheet metal is 20 in. wide. It is made into a ...

calculus - A long rectangular sheet of metal, 12 inches wide, is to be made into...

Pre-Calc) - a piece of rectangular sheet metal is 20 in wide. It's to be made ...

Geometry - 1. An airplane is flying at 36,000 feet directly above Lincoln, ...

math - You are designing a rain gutter made from a piece of sheet metal that is...

mathematics - Please help me answer this question; 1.A metal gutter open at the ...

Math Wrod Problem - 1. A long strip of copper 8 inches wide is to be made into a...

Math - Algebra - In a thin rectangular tin sheet 8x12 sheet, you have to cut a ...

math - Donald wants to build an aquarium with internal volume of 1 m^3 that made...