Dividing vs Subtracting to Solve Equations w/1 Variable

Multiplying by the reciprocal is also acceptable, but can be more difficult to integrate. In summary, when dealing with equations that are separable, it is best to divide rather than subtract in order to get all terms with one variable to one side.
  • #1
find_the_fun
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If you have the equation \(\displaystyle \frac{dx}{dt}=4(x^2+1)\) I sometimes get confused if i should should subtract \(\displaystyle 4(x^2+1)\) from both sides or multiply by it's reciprocal. If I subtract from both sides then I'd have 0 on the right side and that would give a different answer after integration but mathematically why would it be wrong?
 
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  • #2
Re: Dividing vs subtracting to get all terms with one variable to one side of equation

find_the_fun said:
If you have the equation \(\displaystyle \frac{dx}{dt}=4(x^2+1)\) I sometimes get confused if i should should subtract \(\displaystyle 4(x^2+1)\) from both sides or multiply by it's reciprocal. If I subtract from both sides then I'd have 0 on the right side and that would give a different answer after integration but mathematically why would it be wrong?

Since for all real x is $ 4\ (x^{2} + 1) > 0$ You can divide both sides by $ 4\ (x^{2} + 1)$ without danger and then integrate separately in x and y...

Kind regards

$\chi$ $\sigma$
 
  • #3
Re: Dividing vs subtracting to get all terms with one variable to one side of equation

find_the_fun said:
If you have the equation \(\displaystyle \frac{dx}{dt}=4(x^2+1)\) I sometimes get confused if i should should subtract \(\displaystyle 4(x^2+1)\) from both sides or multiply by it's reciprocal. If I subtract from both sides then I'd have 0 on the right side and that would give a different answer after integration but mathematically why would it be wrong?

Since this equation is separable, the best approach would be to divide so that you can separate variables, and as chisigma pointed out, you can do this without worrying about division by zero, and thus you are eliminating no solutions.
 

FAQ: Dividing vs Subtracting to Solve Equations w/1 Variable

What is the difference between dividing and subtracting to solve equations with one variable?

The main difference between dividing and subtracting to solve equations with one variable is the operation used to isolate the variable. When dividing, you are dividing both sides of the equation by the same number, while when subtracting, you are subtracting the same number from both sides of the equation.

When should I use dividing to solve equations with one variable?

Dividing is typically used when you have a variable that is being multiplied by a number and you want to isolate the variable. For example, if you have the equation 4x = 16, you would divide both sides by 4 to isolate x and solve for its value.

When should I use subtracting to solve equations with one variable?

Subtracting is typically used when you have a variable that is being added to a number and you want to isolate the variable. For example, if you have the equation x + 5 = 11, you would subtract 5 from both sides to isolate x and solve for its value.

Is one method more effective than the other?

Both dividing and subtracting can be effective in solving equations with one variable. The method you choose may depend on the specific equation and what operation is being performed on the variable. It is important to carefully consider the equation and choose the method that will result in the simplest solution.

Can I use a combination of dividing and subtracting to solve an equation with one variable?

Yes, you can use a combination of dividing and subtracting to solve an equation with one variable. This may be necessary if the equation involves multiple operations on the variable. Just make sure to perform the same operation on both sides of the equation to maintain balance.

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