Solving Basic Equations: Tips & Tricks

[cording12]

Homework Statement

Solve each of the following equations. This is part of a practice mock test I have for an exam so I have all the answers but they aren't lining up somewhere. I got a) right but b) and c) wrong

Homework Equations

a)4x+6=18
b)5x+7=7x-9
c)1/x+2 = 7 (giving answer rounded to 4 decimal places)

The Attempt at a Solution

The first was easy, the rest though :/
a:
4x+6=18
4x=12
x=3

b:
5x+7 = 7x-9
-2X = -2
X= 4


c:
1/x+2 = 7
x+2 = (7*1)
x=5

the answer they got was -1.8571...

Please help guys this basic stuff is killing me! I can do that advanced stuff no problem (this is for a degree in Engineering) but this basic stuff is a nightmare!

 

[Mark44]

Homework Statement

Solve each of the following equations. This is part of a practice mock test I have for an exam so I have all the answers but they aren't lining up somewhere. I got a) right but b) and c) wrong

Homework Equations

a)4x+6=18
b)5x+7=7x-9
c)1/x+2 = 7 (giving answer rounded to 4 decimal places)

You should write this as 1/(x + 2) = 7. Without the parentheses, 1/x + 2 means (1/x) + 2, which is not what you intend.

The Attempt at a Solution

The first was easy, the rest though :/
a:
4x+6=18
4x=12
x=3

b:
5x+7 = 7x-9
-2X = -2
X= 4

Divide both sides of the equation -2x = -2 by -2. The solution is not x = 4.

c:
1/x+2 = 7
x+2 = (7*1)
x=5

Again, write the equation as 1/(x + 2) = 7. Now, if two numbers are equal, their reciprocals are equal, so the next equation is
x + 2 = 1/7
Can you finish this?

the answer they got was -1.8571...

Please help guys this basic stuff is killing me! I can do that advanced stuff no problem (this is for a degree in Engineering) but this basic stuff is a nightmare!

 

[eumyang]

b:
5x+7 = 7x-9
-2X = -2
X= 4

Divide both sides of the equation -2x = -2 by -2. The solution is not x = 4.

Not only that, but from
5x+7 = 7x-9,
when you move terms around, you don't get
-2x = -2.