Asked by Mike

Solve the equation system exactly.
21x + 6y = 7
7x + 3y = 3

What does it mean equation system? It gives two formulas so I'm not sure. (Sorry this is typically in swedish and it's called 'ekvationssystemet' so I'm unsure for this one) Is it about the substitution method or something more?
Answered by Mike
21x+6y=7
1(21x+6y)=1*7
21x+6y=7

7x+3y=3
-3(7x+3y)=-3*3
-21x-9y=-9


Then

21x+6y-21x-9y=-9+7
-3y=-2
y=-2/-3
y=2/3

and for X

21x+6y=7
21x+6(2/3)=7
21x+4=7
21x=3
x=3/21
x=1/7

Does that seem correct?
Answered by oobleck
who's to say?
Does x = 1/7 and y = 2/3 work in both equations?

21x + 6y = 7
7x + 3y = 3

21(1/7) + 6(2/3) = 3+4 = 7
7(1/7) + 3(2/3) = 1+2 = 3

So, it looks correct.
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