in geometry and algebra, what is the equation for substitution?

Question

i am really confused. how do i use substitution?

Answer 1

substitution is not an equation, it's a thing you do with equations.

suppose you know A = 2B and also that A + B = 12. then you can SUBSTITUTE the expression that A is equal to for A:

(A) + B = 12
(2B) + B = 12
3B = 12
B = 4

and then A = 2B = 2(4) = 8

Answer 2

for one equation, set it equal to either y= or x=

so if you're problems are:
x + y = 4
4x + 2y = 16

you should use the first one and set it for y= to solve for x, or set it for x= to solve for y. let's solve for y:

y = 4 - x *because i subtracted x from each side*

then, you would fill in 4-x into the other equation, whereever you see a y:
4x + 2(4-x) = 16 *then distribute*
4x + 8 - 2x = 16 *combine like terms*
2x + 8 = 16 *subtract 8 from each side*
2x = 8 *divide by 2 on each side*
x = 4

then you want to go to the original equation and fill in 4 for x:
(4) + y = 4 *subtract 4 from each side*
y = 0


to check, just fill in your answers to each equation and see if it works: [answers: x = 4, y=0]

4 + 0 = 4 --> 4 = 4 true
4(4) + 2(0) = 16 --> 16 + 0 = 16 --> 16 = 16 true



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Answer 3

you make or they give you 2 equations
you isolate for 1 varible in one of the equations
sub the isolated varible equation into the other equation

for example

x+y=1 and 2x-y=9

isolate for 1 variable
y=1-x
sub y into the other equation
2x-(1-x)=9
simpllify and solve for x
once x is found then sub x back into one of the original equations to find y