Question

10. Fill in the missing reasons for the following two-column proof:
Given: 5x + 1 = 21
Prove: x = 4

1) 5x + 1 = 21 1) Given
2) 5x = 20 2) _________________________
3) x = 4 3) _________________________

Answer 1

5x=21-1
5x=20
x=20/5
x=4

Answer 2

thats understood but i need to write a two column proof

Answer 3

1) 5x + 1 = 21 1) Given
2) 5x = 20 2) Subtracting 1 from both sides
3) x = 4 3) Dividing both sides by 5

Answer 4

you have to use one of the properties of equality to fill in a two column proof.

Answer 5

Something like
2) Subtracting the same number from both sides of an equation keeps both sides equal.
?

Answer 6

http://www.basic-mathematics.com/properties-of-equality.html

Answer 7

I found this link:
http://hotmath.com/hotmath_help/topics/properties-of-equality.html

So for step 2
Subtraction Property
For all real numbers x, y, and z, if x = y, then x – z = y – z.
This property allows you to balance and solve equations involving real numbers.

Answer 8

For step 3
Division Property
For all real numbers x, y, and z, if x = y, and z ≠ 0, then x/z = y/z.
This property allows you to balance and solve equations involving real numbers.

Answer 9

okay then 3 would be...?

Answer 10

See my last posting

Answer 11

im lost.

Answer 12

because wouldnt that be for step 2

Answer 13

I don't know why you are lost.
Step 2 pertains to subtraction and Step 3 pertains to division.

Answer 14

I can fill in the two column proof for all 3 steps if you want

Answer 15

2 actually isnt substraction its division of 20/5 and 3 seems to be the solution by some property

Answer 16

1) 5x + 1 = 21 1) Given
2) 5x = 20 2) Subtraction Property
For all real numbers x, y, and z, if x = y, then x – z = y – z.

3) x = 4 3) Division Property
For all real numbers x, y, and z, if x = y, and z ≠ 0, then x/z = y/z.

In step 2 we are subtracting 1 from both sides.
In step 3 we are dividing both sides by 5

Answer 17

but there was no subtraction done in 2. it was division...

Answer 18

Maybe it is better to add one more line to Step 2

1) 5x + 1 = 21 1) Given

Then we subtract 1 from both sides
2) 5x = 20 2) Subtraction Property
For all real numbers x, y, and z, if x = y, then x – z = y – z.

We could add one more line to step 3 also

Answer 19

but it would then be incorrect due to the fact there's only 3 lines lool

Answer 20

Okay time to add another instruction

1) 5x + 1 = 21 1) Given

Then we subtract 1 from both sides
5x + 1 -1 = 21 -1
which gives us
2) 5x = 20 2) Subtraction Property
For all real numbers x, y, and z, if x = y, then x – z = y – z.

Answer 21

ohh okay

Answer 22

i still dont get it though.

Answer 23

Well I have explained it about as much as I have.
Do you understand about 2 column proofs?

Answer 24

ughh i give up you get a medal for trying so hard!

Answer 25

Well thanks for the medal.
I could explain even more but maybe I should quit.
If you do find someone else to help you by all means direct them to this page.