MHB Find the area of the red region

  • Thread starter Thread starter anemone
  • Start date Start date
  • Tags Tags
    Area
AI Thread Summary
The discussion focuses on calculating the area of a red region within a parallelogram, where the areas of adjacent green regions are provided as 8 unit², 10 unit², 72 unit², and 79 unit². Participants analyze the relationships between these areas to derive the area of the red region. The total area of the parallelogram is implied to be the sum of the green regions plus the red region. By applying geometric principles and area calculations, the participants aim to find the value of the red region. The conclusion emphasizes the importance of understanding area relationships in geometric figures.
anemone
Gold Member
MHB
POTW Director
Messages
3,851
Reaction score
115
The diagram below (which is not drawn to scale) shows a parallelogram. The area of the green regions are 8 unit² , 10 unit² , 72 unit² and 79 unit² respectively. Find the area of the red region.

[TIKZ]
\coordinate (A) at (0,0);
\coordinate (B) at (8,0);
\coordinate (C) at (12,0);
\coordinate (D) at (12.75,3);
\coordinate (E) at (14,8);
\coordinate (F) at (6,8);
\coordinate (G) at (2,8);
\coordinate[label=above: \huge 79] (P) at (4.5,3);
\coordinate[label=above: \huge 72] (Q) at (9.5,6);
\coordinate[label=above: \large 8] (R) at (8.5,1.2);
\coordinate[label=above: \large 10] (S) at (11,2.9);
\draw (A) -- (C)-- (E) -- (G) -- (A);
\draw (A) -- (F);
\draw (A) -- (D);
\draw (B) -- (F);
\draw (B) -- (E);
\draw (D) -- (G);
\draw[fill=teal] (0,0) -- (7.564,1.745) -- (6.513,5.949) -- (4.983,6.644);
\draw[fill=teal] (6,8) -- (6.508,5.931) -- (10.93,3.85) -- (14,8);
\draw[fill=teal] (8,0) -- (7.564,1.76) -- (9.674,2.25);
\draw[fill=teal] (10.92,3.89) -- (12.75,3) -- (9.674,2.25);
\draw[fill=teal] (4.5,3) node[text=pink] {\huge 79};
\draw[fill=teal] (9.5,6) node[text=pink] {\huge 72};
\draw[fill=teal] (8.5,1.2) node[text=pink] {\large 8};
\draw[fill=teal] (11,2.9) node[text=pink] {\large 10};
\draw[fill=magenta] (2,8) -- (4.983,6.644) -- (6,8);
[/TIKZ]
 
Last edited:
Mathematics news on Phys.org
Area of triangle
 
[TIKZ]
\coordinate (A) at (0,0);
\coordinate (B) at (8,0);
\coordinate (C) at (12,0);
\coordinate (D) at (12.75,3);
\coordinate (E) at (14,8);
\coordinate (F) at (6,8);
\coordinate (G) at (2,8);
\coordinate[label=above: \huge 79] (P) at (4.5,3);
\coordinate[label=above: \huge 72] (Q) at (9.5,6);
\coordinate[label=above: \large 8] (R) at (8.5,1.2);
\coordinate[label=above: \large 10] (S) at (11,2.9);
\coordinate[label=above: \huge A] (M) at (2.5,5);
\coordinate[label=above: \huge B] (N) at (6,0.48);
\coordinate[label=above: \huge C] (Z) at (5.8,6.8);
\coordinate[label=above: \huge D] (J) at (8.5,3.2);
\coordinate[label=above: \huge E] (K) at (10.5,0.9);
\coordinate[label=above: \huge F] (I) at (12.2,4.2);
\draw (A) -- (C)-- (E) -- (G) -- (A);
\draw (A) -- (F);
\draw (A) -- (D);
\draw (B) -- (F);
\draw (B) -- (E);
\draw (D) -- (G);
\draw[fill=teal] (0,0) -- (7.564,1.745) -- (6.513,5.949) -- (4.983,6.644);
\draw[fill=teal] (6,8) -- (6.508,5.931) -- (10.93,3.85) -- (14,8);
\draw[fill=teal] (8,0) -- (7.564,1.76) -- (9.674,2.25);
\draw[fill=teal] (10.92,3.89) -- (12.75,3) -- (9.674,2.25);
\draw[fill=teal] (4.5,3) node[text=pink] {\huge 79};
\draw[fill=teal] (9.5,6) node[text=pink] {\huge 72};
\draw[fill=teal] (8.5,1.2) node[text=pink] {\large 8};
\draw[fill=teal] (11,2.9) node[text=pink] {\large 10};
\draw[fill=magenta] (2,8) -- (4.983,6.644) -- (6,8);
[/TIKZ]

If we look at the parallelogram in such a way that the horizontal sides are the base, then we have

$\normalsize \text{Area of B}+\text{Area of C}+79+\text{Area of E}+\text{Area of F}+10=\text{Area of A}+\text{Area of red region}+72+8+\text{Area of D}$

If we look at the parallelogram in such a way that the slanted sides are the base, then we have

$\normalsize \text{Area of B}+\text{Area of E}+8+\text{Area of F}+\text{Area of C}+72+\text{Area of red region}=\text{Area of A}+79+10+\text{Area of D}$

Subtracting the below from the above we get

$ 9-\text{Area of red region}=-9+\text{Area of red region}\\ \\ \therefore \text{Area of red region}=9$
 
Seemingly by some mathematical coincidence, a hexagon of sides 2,2,7,7, 11, and 11 can be inscribed in a circle of radius 7. The other day I saw a math problem on line, which they said came from a Polish Olympiad, where you compute the length x of the 3rd side which is the same as the radius, so that the sides of length 2,x, and 11 are inscribed on the arc of a semi-circle. The law of cosines applied twice gives the answer for x of exactly 7, but the arithmetic is so complex that the...
Thread 'Video on imaginary numbers and some queries'
Hi, I was watching the following video. I found some points confusing. Could you please help me to understand the gaps? Thanks, in advance! Question 1: Around 4:22, the video says the following. So for those mathematicians, negative numbers didn't exist. You could subtract, that is find the difference between two positive quantities, but you couldn't have a negative answer or negative coefficients. Mathematicians were so averse to negative numbers that there was no single quadratic...
Thread 'Unit Circle Double Angle Derivations'
Here I made a terrible mistake of assuming this to be an equilateral triangle and set 2sinx=1 => x=pi/6. Although this did derive the double angle formulas it also led into a terrible mess trying to find all the combinations of sides. I must have been tired and just assumed 6x=180 and 2sinx=1. By that time, I was so mindset that I nearly scolded a person for even saying 90-x. I wonder if this is a case of biased observation that seeks to dis credit me like Jesus of Nazareth since in reality...

Similar threads

Replies
2
Views
1K
Replies
2
Views
1K
Back
Top