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Special Right Triangles. One of the good things about math is that you can recreate it yourself, if you can remember the basics. So let’s pretend you suddenly have a Special Right Triangles test, but only vaguely remember anything about them. Special Right Triangles. YIKES!. Don’t Panic.

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Special right triangles

Special Right Triangles

One of the good things about math is that you can recreate it yourself, if you can remember the basics.

So let’s pretend you suddenly have a Special Right Triangles test, but only vaguely remember anything about them.


Special right triangles1

Special Right Triangles

YIKES!

Don’t Panic.


Special right triangles2

Special Right Triangles

Looking carefully, I see there are only two kinds of right triangles here….


Special right triangles3

Special Right Triangles

… and the 45-45-90.

There is the 30-60-90….


Special right triangles4

Special Right Triangles

Let’s deal with this one first...

1

1

And instead of dealing with x, let’s make it easier and have the length of the legs be 1.


Special right triangles5

Special Right Triangles

Ok… so, it’s a right triangle… and the first thing I think of when I see a right triangle is…..

1

1

THE PYTHAGOREAN THEOREM!


Special right triangles6

1 + 1=c2

Special Right Triangles

2=c2

c = sqr root 2

…and if I want the hypotenuse, all I have to do is solve 12 + 12 =c2.

1

1


Special right triangles7

Special Right Triangles

• r

sqr root 2

…and every triangle that has the same angles as this one will be similar to it…

1 • r

1

1

1 • r

…which means that they will all be dilations of this one… with some zoom factor/ratio that I can call r.


Special right triangles8

Special Right Triangles

• r

sqr root 2

OK… Now I’m ready… bring on the problems.

1 • r

1

1

1 • r


Special right triangles9

Special Right Triangles

• r

sqr root 2

This one is 45-45-90.

The length of one leg is 18… which means 18 = 1 • r.

1 • r

1

1

1 • r

So it’s easy enough to figure out that 18 = r.

And since the hypotenuse is r • sqr root 2…


Special right triangles10

Special Right Triangles

• r

sqr root 2

x = 18 • sqr root 2

1 • r

1

1

1 • r


Special right triangles11

Special Right Triangles

• r

sqr root 2

NEXT!

This one is also 45-45-90.

1 • r

1

1

1 • r

In fact, the only difference is that r = 3 • sqr root 2

And since the hypotenuse is r • sqr root 2…


Special right triangles12

Special Right Triangles

• r

sqr root 2

1 • r

1

1

1 • r

x = (3 • sqr root 2) • sqr root 2

x = 3 • (sqr root 2 • sqr root 2)

x = 3 • 2

x = 6


Special right triangles13

Special Right Triangles

• r

sqr root 2

NEXT!

This one is also 45-45-90.

1 • r

1

1

1 • r

But we’re given the hypotenuse, instead of a leg!

We know the hypotenuse is r • sqr root 2…


Special right triangles14

Special Right Triangles

• r

sqr root 2

1 • r

1

1

1 • r

18 = r • sqr root 2

18• sqr root 2 = r • sqr root 2• sqr root 2

18• sqr root 2= r • 2

9• sqr root 2= r … and so does x


Special right triangles15

600

Special Right Triangles

600

600

Let’s take on the 30-60-90 now.

This one starts off as an equilateral triangle… with all sides equal… and all angles equal to 60 degrees.

Then, we cut it in half.


Special right triangles16

Special Right Triangles

300

300

2

2

600

600

1

1

So now, the two angles at the top are 30 degrees each.

And if the original sides of the equilateral triangle had a length of two, the bottom is cut in half, too!


Special right triangles17

Special Right Triangles

300

2

600

1

Now, let’s just look at the half we care about… the 30-60-90 triangle.

Notice that the hypotenuse is twice as long as the side opposite the 300 angle.

That’s always going to be true!


Special right triangles18

12 + h2 =22

1 + h2 =4

Special Right Triangles

300

2

h2 =3

h

h = sqr root 3

600

1

What about the height?

This is a job for…..

THE PYTHAGOREAN THEOREM!

a2 + b2 =c2


Special right triangles19

Special Right Triangles

300

2

• r

r •

sqr root 3

600

1

• r

Because every 30-60-90 triangle will be similar to this one…

The sides will always be proportional to these sides!

So we are all set to get started.


Special right triangles20

Special Right Triangles

300

300

2

• r

r •

sqr root 3

600

1

• r

The missing angle is 300.

We are given the length of the side opposite that angle, so r = 8.

The hypotenuse, y, is equal to 2r… or 16.

The side across from the 600 angle has to be r • sqr root 3…

so x = 8 • sqr root 3


Special right triangles21

Special Right Triangles

300

2

• r

r •

sqr root 3

600

1

• r

Let’s do another.


Special right triangles22

Special Right Triangles

300

2

• r

r •

sqr root 3

600

1

• r

The hypotenuse, which has to be 2 • r, is equal to 11.

That means r, the side opposite the 300 angle,has to be 5.5….

and so x = 5.5.

The side across from the 600 angle has to be r • sqr root 3…

so y = 5.5 • sqr root 3


Special right triangles23

Special Right Triangles

300

2

• r

r •

sqr root 3

600

1

• r

Bring on the next one!


Special right triangles24

Special Right Triangles

300

2

• r

r •

sqr root 3

300

600

600

1

• r

Since this is an isoceles triangle, the other base angle is also 600.

And the half-angle on the right is 300.

And we can focus on just the part we care about!


Special right triangles25

Special Right Triangles

300

2

• r

r •

sqr root 3

300

600

600

1

• r

The hypotenuse, which has to be 2 • r, is equal to 20.

That means r, the side opposite the 300 angle,has to be 10….

and so y = 10.

The side across from the 600 angle has to be r • sqr root 3…

so x = 10 • sqr root 3


Special right triangles26

Special Right Triangles

300

2

• r

r •

sqr root 3

600

1

• r

And, finally….


Special right triangles27

Special Right Triangles

300

2

• r

r •

sqr root 3

600

1

• r

This time, we are given the length of the side opposite the 600 angle, which has to be r • sqr root 3.

If 12 = r • sqr root 3…

12 • sqr root 3 = (r • sqr root 3)• sqr root 3

12 • sqr root 3 = r • (sqr root 3 • sqr root 3)

12 • sqr root 3 = r • 3

4 • sqr root 3 = r


Special right triangles28

Special Right Triangles

300

2

• r

r •

sqr root 3

600

1

• r

Since r = 4 • sqr root 3…

and that is the side opposite the 300 angle…

x = 4 • sqr root 3


Special right triangles29

Special Right Triangles

300

2

• r

r •

sqr root 3

600

1

• r

And, again, since r = 4 • sqr root 3…

and the hypotenuse (y) has to be twice as long…

y = 8 • sqr root 3


Special right triangles30

sqr root 2

Special Right Triangles

300

2

• r

r •

sqr root 3

1 • r

1 • r

600

1

• r

So, if you ever have to answer questions about Special Right Triangles,

now you know that you can create the “formulas” from scratch,

just by using the Pythagorean Theorem.