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Lesson 3: One-step addition & subtraction equations

In this math lesson, we learn to solve simple equations with one variable. We isolate the variable by removing other terms on the same side. For example, if a + 5 = 54, we subtract 5 from both sides to find a = 49. Finally, we check our solution by substituting the value back into the original equation. Created by Sal Khan.

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• why is there a pic of queen Elizabeth just chillin'?
• No idea maybe he just thought it'd get our attention, thus leading him to displaying it.
• what do you do if the variable is in the midlle of both numbers for example -10.74=u- (-11)
u-(-11) = -10.74
You can switch the sides of an equation. Now the "u" is not in the "middle" of the numbers. Though, I would argue it was never in the middle of the numbers because the equals symbol is really separating the "u" from the number on the left side.
• How do I fix an equation like 44-q = 11 It's simply a true / false answer in my pre-algebra book. The answer is simple, it's 33. However, I do not know how to configure the equation. The example in the video shows the variable minus the number equals the difference. But what happens when the number is first and the variable is subtracted from the number? How can I configure this equation so that future equations that can not simply be solved without showing the work can be solved?
• You have 2 options...
Option 1
Subtract 44 from both sides: -q = -33
Then, you need to divide both sides by -1 to change -q into just q: q = 33

Option 2
Add q to both sides: 44 = 11 + q
Then subtract 11 from both sides: 33 = q

Hope this helps.
• Why do some numbers get canceled out?
• Some got canceled out because when if you do something like subtraction, you will get 0. If you do division, you will get a 1, and it is already assumed there is a 1 in front of a variable.
• what is the equation for x?
3(x+2)=2(2-x)
• 3(x+2)=2(2-x) ...........original equation needs modification to isolate x
3x+6=4-2x ..........distribute
3x+6-6=4-6-2x ......subtract 6 from both sides
3x=-2-2x
3x+2x=-2-2x+2x ......once that is done add 2x to both sides
5x=-2
5x/5=-2/5 ...........divide by 5 on both sides to move the 5 over
x=-2/5
• when we scheck the answer are teacher tough us away longer way to do that
• you said subtract 54 from the right side at 0.59
• Is this going to be easy
• hopefully so
• why do you need to subtract or add numbers to both sides when you are just getting number off from one side?
• If you just do the operation to one side, the equation is no longer equal (in balance).
For example: 2+5 = 11-4
I've used only numbers so you can see both sides currently = 7. The equation is in balance.
Add 4 to only right side and you get: 2+5 = 11
The equation is no longer equal. I've performed an invalid operation to the equation.

Note: Some teachers teach that you pick up the number and move it to the other side by changing its sign. For example, change the "-4" into "+4" and put it on the left side:
2+5+4 = 11
But, to achieve this, you still have added 4 to both sides. It was just not written out.
Hope this helps.