First, you have to do some factorization
60 = {1,2,3,4,5,6,10,12,15,20,30,60}
72 = {1,2,3,4,6,8,9,12,18,24,36,72}
the GCF is 12
now we find the number that you multiply by 12 to get 60 and another number to get 72.
12 x 5 = 60
12 x 6 = 72
now we notice if you add 60 + 72, we can now tell that it also equals (12)(5)+(12)(6)= 12(5+6)
The Answer is b: x = 18, y = -20
Proof:
Solve the following system:
{4 x + 3 y = 12 | (equation 1)
{7 x + 5 y = 26 | (equation 2)
Swap equation 1 with equation 2:
{7 x + 5 y = 26 | (equation 1)
{4 x + 3 y = 12 | (equation 2)
Subtract 4/7 × (equation 1) from equation 2:
{7 x + 5 y = 26 | (equation 1)
{0 x+y/7 = (-20)/7 | (equation 2)
Multiply equation 2 by 7:
{7 x + 5 y = 26 | (equation 1)
{0 x+y = -20 | (equation 2)
Subtract 5 × (equation 2) from equation 1:
{7 x+0 y = 126 | (equation 1)
{0 x+y = -20 | (equation 2)
Divide equation 1 by 7:
{x+0 y = 18 | (equation 1)
{0 x+y = -20 | (equation 2)
Collect results:
Answer: {x = 18, y = -20
