SOLUTION: What is the best first step to solve the system using elimination? And how do you solve it? x � 5y = 4 3x + 7y = �17 multiply the first equation by �3 multiply the seco

Question 361966: What is the best first step to solve the system using elimination? And how do you solve it?
x � 5y = 4
3x + 7y = �17
multiply the first equation by �3
multiply the second equation by 3
solve for x in the first equation
solve for y in the second equation
Answer by Theo(13342) (Show Source): You can put this solution on YOUR website!
using elimination, the best first step is multiply the first equation by -3.

multiply the second equation by 3 doesn't do anything to eliminate one of the unknowns.

solving for x in the first equation or solving for y in the second equation are the substitution method, not the elimination method.

your original equations are:

x - 5y = 4
3x + 7y = -17

multiply the first equation by -3 to get:

-3x + 15y = -12
3x + 7y = -17

add both equations together to get:

22y = -29

divide both sides of the equation by 22 to get:

y = (-29/22)

substitute in first original equation to get:

x - 5y = 4 becomes x - 5 * (-29/22) = 4 becomes x - (-145/22) = 4 becomes x + (145/22) = 4.

subtract (145/22) from both sides of the equation to get:

x = 4 - (145/22) which becomes x = (88/22) - (145/22) which becomes x = (-57/22)

your solutions are:

x = (-57/22)

y = (-29/22)

substitute for x and y in both original equations and you will see that they are both true which means the solution is good.

the equations being true means that the left side of the equation is equal to the right side of the equation.

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