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# 4 math questions i need help in, (Geometry)

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6    Can anybody help? Thanks!

Jun 29, 2018

#1
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1) for this to be a right triangle, the other side would have to be 12, a 5/12/13 triangle.

so 5*12*1/2 for area is 30

2) the diagonals of a polygon are n(n-3)/2 this means (n-3)/2 = 10 so n = 23

3) the volume of the first block is 140 and cost $40 40/140 money per cm^3 is the cost the volume of the second figure is 12*42*45 or 22680 22680 times 40/140 is$6480

4) the perimiter is 98 and two of the sides are equal.

thus we have two true equations.

if the sides that are equal, called x, and the base is called, y

then 2x+y = 98  and 35^2 + (y/2)^2 = x^2

using substitution, y=98-2x we get 35^2 + [(98-2x)/2]^2 = x^2

solving for x we get, x = 37

if x = 37 then the base is 98- 2(37) = 24

now area of triangle formula (24 * 35)/2 = 420

Jun 29, 2018
edited by Guest  Jun 30, 2018
edited by Guest  Jun 30, 2018
#3
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Thank you!!!!

AWESOMEEE  Jun 29, 2018
#4
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CPhill: The answer in 3 is wrong!!!! You don't divide cubic cm by money. You divide:

$40 / 140 =$0.2857.....per cubic cm.

$0.2857..... x 22,680 cubic cm =$6,480 - cost of  the larger block of wood.

Or: [22,680 / 140] x $40 =$6,480.

Guest Jun 29, 2018
edited by Guest  Jun 29, 2018
#2
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3)  You reversed the cost!!

It should be: $40/140 x 22, 680 =$6,480 - Cost of the larger block.

Jun 29, 2018
#5
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Here's 3

The total  volume  of the  first  prism is  ( 4 * 7 * 5)  = 140 cm^3

So....the price per cubic centimeter  is   4000 cents/140 cm^3   ≈  28.6 cents / cm^3

And the volume  of the second prism is  (12 * 42 * 45)  = 22680 cm^3

So...the price of the second prism (block)  is just

22680 cm^3  *  28.6 cents / cm^3 =  648648 cents  ≈   \$6486.48   Jun 29, 2018
#6
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The formula to find the number of diagnols in a polygon is $$\frac{n(n-3)}{2}$$.

Since we have 10n for the number of diagnols, we get: $$\frac{n(n-3)}{2}=10n$$.

Taking 2 to the other side, we get: $$n(n-3)=20n$$.

Dividing n on both sides, we get: $$n-3=20$$

This means that $$\boxed{n=23}$$.  Jun 29, 2018