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Mathematics 12 Online
woolyfrog:

http://prntscr.com/jgsx9s Geometry help

woolyfrog:

@Elsa213

woolyfrog:

it's blank

Hero:

|dw:1526084336024:dw|

woolyfrog:

we use the square area formula?

Hero:

We find the area of the square then subtract out the area of the triangles that are not shaded.

Hero:

Pretty easy to do, just hang on a minute.

Hero:

|dw:1526084460439:dw|

Hero:

Okay, so basically, now we can easily find the area of the square, then find the areas of each triangle then perform the following calculation: \(\text{Area of Shaded Figure = Area of Square - Total Area of Unshaded Figures}\)

Hero:

There is another way to do it. Let me post that.

woolyfrog:

ok

Hero:

|dw:1526084764845:dw|

Hero:

Find the area of all those right triangles plus the area of the rectangle. Let's number them:

Hero:

|dw:1526084865424:dw|

woolyfrog:

we can do the first way xD

woolyfrog:

or the second

Hero:

So we can find the area of each individual shaded figure to find the total shaded area. \(A_t = A_1 + A_2 + A_3 + A_4 + A_5 + A_6\)

Hero:

You know the formulas for area of a triangle and area of a rectangle correct?

woolyfrog:

yes

woolyfrog:

we can do the first one

Hero:

Actually, it's more efficient to do the second method.

woolyfrog:

Okay let's do that one lol

Hero:

Actually, I was hoping that you would be inspired to try this on your own and post your attempt here using that formula I gave you above. See if you can find the areas of each small figure and post here: \(A_1 = ?\) \(A_2 = ?\) \(A_3 = ?\) \(A_4 = ?\) \(A_5 = ?\) \(A_6 = ?\)

woolyfrog:

ok

woolyfrog:

the base of the number 1 triangle is 5 and the height is 2 or 3?

Hero:

It really doesn't matter to be honest. Either of the legs of the triangles can be considered base or height. As long as you're using the formula \(A = \dfrac{bh}{2}\) to calculate the area of the triangles

woolyfrog:

yeah I'm using that formula

woolyfrog:

how do I find the base and height of a triangle?

Hero:

You measure the lengths of the segments for both legs of a right triangle. For example for Triangle 1, Leg 1 = | 1 - (-5)| = |1 + 5| = | 6 | = 6

woolyfrog:

leg 2 1 -(-3) = 1+3 = 4

Hero:

You can also just count squares as well which would be easier to do mentally

woolyfrog:

did i do it correct?

woolyfrog:

with the second leg

Hero:

If you count the squares, you will see that the measure of Leg 2 is just 3 units.

woolyfrog:

oh I thought i had to your math thing lol

woolyfrog:

the area is 12

woolyfrog:

my bad I was writing

Hero:

The "math thing" I did is called absolute value. It's just the computation used to find the length of a segment on an xy plane. In this case, the leg occurs vertically, so you would write Length of Leg 2 = |\(y_2 - y_1| = | 0 - (-3)| = | 0 + 3| = | 3 | = 3\)

woolyfrog:

The area is 5 for triangle number 2

Hero:

How did you get 5 for the area of triangle 2? Mind showing the work you did to come up with that?

Hero:

Did you calculate the length of each leg first?

woolyfrog:

i counted the squares that had shade on them.

Hero:

I would recommend that you count the squares rather than use the formula

woolyfrog:

i cant draw rip

Hero:

|dw:1526086289077:dw|

woolyfrog:

yeah that part is 5

woolyfrog:

I thought that side was the base cause the triangle is sideways

Hero:

First count the vertical squares. You get 5 for that. Then count the horizontal squares. You get 2 for that

Hero:

But yeah, it's five for the area.

woolyfrog:

ok lol wow

Hero:

You're correct. So far we have: \(A_1 = 9\) \(A_2 = 5\)

woolyfrog:

A3= 3

woolyfrog:

A4=3

woolyfrog:

A5=2

Hero:

Very good

woolyfrog:

RECTANLGE = 20

Hero:

So \(A_6 = 20\) Okay, time to add them all up to get the total area.

Hero:

So \(A_t \\= A_1 + A_2 + A_3 + A_4 + A_5 + A_6 \\= 9 + 5 + 3 + 3 + 2 + 20 \\= 14 + 6 + 22 \\= 20 + 22 \\= 42\)

Hero:

The area of the first triangle is 9. Go back and calculate

woolyfrog:

oh i thought it was 12

Hero:

Calculate it now and see what you get. Clearly the lengths of each leg are 6 and 3.

woolyfrog:

back my laptop wouldn't allow me to type nothing like it let me do nothing

woolyfrog:

10/10 grammar

woolyfrog:

yea it's 9

woolyfrog:

i put the height 4 on accident instead of 3

woolyfrog:

we did it!

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