When you solve the equation x + 9=15, how do you know what number to subtract from both sides? Why is it important to subtract the same number from both sides of the equation?

Question

jack1 · Answer

9
as you want the variable/unknown to exist on one side of the equals sign alone

jack1 · Answer

pretend the equals sign is a seesaw, then visualise what you want to find, then manipulate that side of the equation so it is alone, and as its a seesaw, what you do to one side you must do to the other

anonymous · Answer

what?

jack1 · Answer

x   +   9   =  15
you want the x by itself, as it's the unknown factor

so the equation you want to end up with is:
x      =   something
therefore the steps to get to that are:
there is a +9 on the side with the x, so subtract 9 from both sides (otherwise it wont balance)

left with:
x  +9  -9  =  15  -9
x  =  6

anonymous · Answer

oh thx