Math Is Fun Forum

lisathedork

Member

Registered: 2013-10-24

Posts: 36

Pythagorean Theorem - Geometry

I was having trouble for the last 10 questions of this lesson.
So far, this is what I got.

What is the value of b if...

11.  a=6 and c=12
6^2 + b^2 = 12
6 + b^2 = 12
b^2 = 12 - 6
SQRT b^2 = SQRT 6
b = 6

12. a=18 and c=30
18^2+ b^2 = 30
18 + b^2 = 30
b^2 = 30 - 18
b^2 = 12
SQRT b^2 = SQRT 3.46
b = 3.46

13. a=7 and c=SQRT 85

14. a=1 and c=5

15. a=1 and c=SQRT 2

16. a=10 and c=12

17. a=21 and c=35

18. a=5 and c=18

19. a=6 and c=6(SQRT 2)

20. a=11 and c=12

I'm pretty sure I'm wrong, but if so can you please explain? The example they are showing me in the lesson is very confusing.

[Example 2:

What is the value of b, if c=SQRT 2 and a=1?

First, we plug the numbers into our theorem:

a2 + b2 = c2

12 + b2 = SQRT 22

Then we simplify:

1 + b2 = 2

Then we solve for b:

b2 = 2 - 1

b2 = 1

Take the square root of both sides:

SQRT b2 = SQRT 1

b = 1]

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Pythagorean Theorem - Geometry

hi

What is the value of b if...

11.  a=6 and c=12
6^2 + b^2 = 12
6 + b^2 = 12
b^2 = 12 - 6
SQRT b^2 = SQRT 6
b = 6

That should be 6^2 + b^2 = 12^2 = 144

and 6^2 = 36

So you should have

36 + b^2 = 144

B^2 = 108

b = root(108) = root(36 x 3) = 6root(3)

I'll have a look at the rest and post in a few minutes

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Pythagorean Theorem - Geometry

Looks like you are forgetting to square the numbers.

eg.

12. a=18 and c=30
18^2+ b^2 = 30^2

324 + b^2 = 900

b^2 = 576

b = root 576 = ???

I've got to sign out for a while.  I suggest you have another go at these and post your answers.  If no one else beats me to it, I'll check in a couple of hours.

You could also have a look at this:

http://www.mathsisfun.com/pythagoras.html

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

lisathedork

Member

Registered: 2013-10-24

Posts: 36

Re: Pythagorean Theorem - Geometry

Okay here is what I did but I'm still having trouble with 13, 15, and 19.

11.  a=6 and c=12
6^2 + b^2 = 12^2
36 + b^2 = 144
b^2 = 108
b^2 = SQRT 108

12. a=18 and c=30
18^2 + b^2 = 30^2
324 + b^2 = 900
b^2 = 576
b = 24

13. a=7 and c=SQRT 85
7^2 + b^2 =

14. a=1 and c=5
1^2 + b^2 = 5^2
1 + b^2 = 25
b^2 = 24
b^2 = SQRT 24

15. a=1 and c=SQRT 2

16. a=10 and c=12
10^2 + b^2 = 12^2
100 + b^2 = 144
b^2 = 44
b^2 = SQRT 44

17. a=21 and c=35
21^2 + b^2 = 35^2
441 + b^2 = 1,225
b^2 = 784
b = 28

18. a=5 and c=18
5^2 + b^2 = 18^2
25 + b^2 = 324
b^2 = 299
b^2 = SQRT 299

19. a=6 and c=6(SQRT 2)

20. a=11 and c=12
11^2 + b^2 = 12^2
121 + b^2 = 144
b^2 = 23
b^2 = SQRT 23

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Pythagorean Theorem - Geometry

Hi;

Since

then

so

Can you find b?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

lisathedork

Member

Registered: 2013-10-24

Posts: 36

Re: Pythagorean Theorem - Geometry

Here is what I got:

13. a=7 and c=SQRT 85
7^2 + b^2 = 85
49 + b^2 = 85
b^2 = 36
b = 6

15. a=1 and c=SQRT 2
1^2 + b^2 = SQRT 2
1 + b^2 = SQRT 2
b^2 = 1
b = 1

19. a=6 and c=6(SQRT 2)
6^2 + b^2 = 6(SQRT 2)
36 + b^2 = 24
b^2 = 12 
b^2 = SQRT 12

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Pythagorean Theorem - Geometry

hi

13 and 15 are correct.

for 19 you should have (6root2) squared = 36 x 2 = 72

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

lisathedork

Member

Registered: 2013-10-24

Posts: 36

Re: Pythagorean Theorem - Geometry

Thank you for the help.

19. a=6 and c=6(SQRT 2)
6^2 + b^2 = 6(SQRT 2)
36 + b^2 = 72
b^2 = 36
b = 6

I have more lessons to go!

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Pythagorean Theorem - Geometry

Well done for completing those successfully. 

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob