Question

Angie was given the system of equations. Angie’s work is shown in the table.
7x+y=−12
7x+4y=−6
Where did Angie make an error? Justify your answer.


Step 1; because she should have multiplied the second equation by -1.


Step 2; because she should have eliminated the y-value.


Step 3; because she used substitution incorrectly.


Step 4; because the solution is (2,-26).

Answer 1

Angie made an error because she used substitution incorrectly in step 3.

System of equation

7x + y =−12

7x + 4y = −6

subtract equation(i) from (ii) to eliminate x

Therefore,

3y = 6

y = 6 / 3

y = 2

Therefore,

7x + 2 = -12

subtract 2 from both sides of the equation

7x = -12 - 2

7x = - 14

x = - 14 / 7

x = -2

(-2, 2)

Therefore, Angie use substitution incorrectly in step 3.

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