Question

Solve the following system of equations: 7x - y = 4 and 3x + 2y = 9
A. (2, 10)
B. (1, 3)
C. (5, -3)
D. (4, 24)
I think its A or D im not sure @iGreen. @Loser66

Answer 1

https://www.desmos.com/calculator/lyglb7ciw4

The solution is the point where the two lines cross..and where's that?

Answer 2

@tiffany__ What did you get?

Answer 3

5&3

Answer 4

@iGreen. I think you should guide her solving the problem in algebraic way. Not all of students know how to solve it by graph. I know it is good but graphing is not the best choice for them.

Answer 5

Yes, good point.

Answer 6

Here, we use online graphing tool to draw the equations out in 1 second, on test, they have to draw them by hand and it is not easy to not make a mistake which can lead to wrong answer.

Answer 7

Okay, let's use the substitution method instead.

7x - y = 4

Subtract 7x to both sides:

-y = -7x + 4

Multiply -1 to both sides:

y = 7x - 4

Now plug in 7x - 4 for y in the 2nd equation:

3x + 2(7x - 4) = 9

Distribute 2 into the parenthesis:

3x + 14x - 8 = 9

Combine like terms:

17x - 8 = 9

Add 8 to both sides, what's 9 + 8?

Answer 8

@tiffany__

Answer 9

17

Answer 10

Yep that gives us:

17x = 17

Now divide 17 / 17, what do you get?

Answer 11

1

Answer 12

@iGreen.

Answer 13

Yep, so that's your 'x' term..so which option has a '1' in the beginning?

Answer 14

@tiffany__

Answer 15

b @iGreen.

Answer 16

Yep, so that's your answer. @tiffany__