How do you solve the system $y=3x$ and $2x+y=15$ using substitution?

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Answer 1 · 2017-05-20T02:14:41

See a solution process below:

Step 1) Because the first equation is already solved for $y$ we can substitute $3x$ for $y$ in the second equation and solve for $x$ :

$2x + y = 15$ becomes:

$2x + 3x = 15$

$(2 + 3)x = 15$

$5x = 15$

$(5x)/color(red)(5) = 15/color(red)(5)$

$(color(red)(cancel(color(black)(5)))x)/cancel(color(red)(5)) = 3$

$x = 3$

Step 2) Substitute $3$ for $x$ in the first equation and calculate $y$ :

$y = 3x$ becomes:

$y = 3 xx 3$

$y = 9$

The solution is: $x = 3$ and $y = 9$ or $(3, 9)$

How do you solve the system y=3xy=3x and 2x+y=152x+y=15 using substitution?