Friday

September 19, 2014

September 19, 2014

Posted by **Riana** on Monday, January 28, 2013 at 7:31pm.

- ms sue - I don't know -
**Ms. Sue**, Monday, January 28, 2013 at 7:44pmSorry.

- ms sue -
**Reiny**, Monday, January 28, 2013 at 8:55pmArea = (1/2)base x heigh

= (1/2)(4-x)(2x+3)

= (1/2)(12 + 5x - 2x^2)

d(Area)/dx = (1/2)(5 - 4x)

= 0 for a max area

4x = 5

x = 5/4

using x = 5/4 = 1/25

Maximum Area = (1/2)(4-5/4)(5/2+3) = 7.5625

or appr 7.5625

testing: our answer t= 5/4 = 1.25

let x = 1.24 , area = (1/2)(4-1.24)(2.48+3) = 7.5624 , a bit smaller

let x = 1.26, area = (1/2)(4-1.26)(2.52+3) = 7.5624 , a bit smaller again

all looks good at max area = 7.5625

- ms sue -
**Riana**, Monday, January 28, 2013 at 9:21pmcan you explain how you got 1/2 x 5-4x ?

- ms sue -
**Reiny**, Monday, January 28, 2013 at 9:27pmSince this is a typical Calculus question, I assume you knew Calculus.

I took the derivative.

- ms sue -
**Reiny**, Monday, January 28, 2013 at 9:40pmYou could start with my area equation

area = (1/2)(12 + 5x - 2x^2)

= (1/2)(-2)(x^2 - 5/2x -6)

= -(x^2 - (5/2)x + 25/16 - 25/16 - 6) ----I competed the square

= -( (x - 5/4)^2 - 25/16 - 6)

= (x - 5/4)^2 + 25/16 + 6

= -(x-5/4)^2 + 121/16

area = -(x-5/4)^2 + 121/16

max area = 121/16 or 7.5625

when x = 5/4

just as in my first solution.

**Answer this Question**

**Related Questions**

math problem. help - triangle base is (4-x)cm and its height is (2x+3)cm.what ...

Algebra - How do you find the area of a shaded area in a triangle and assume the...

math - ABC is a right-angled triangle atB. AB=(3x+2)cm and BC=2CM.GIVEN THAT THE...

7th grade math Ms. Sue please last questions! - 15. Find the area of a triangle ...

Algebra - A triangle has an area of 60 in^2. Its base is 10 inches and its ...

7th grade math please help Ms. Sue - 4. Find the area for a triangle: base 14, ...

Algebra Word Problem - COULD SOMEONE PLEASE HELP ME WITH THIS !!!!!!!!!! The ...

Math problem - The area of a triangle is equal to 1/2 the hight times the base. ...

math - The base of a triangle is 5cm greater than the height. The area is 18cm^2...

Pre algebra - find the area of the triangle with base 2 1/5 yards and height 5/8...