Answer:
x = -2 , y = 3
Explanation:
Solve the following system:
{4 x + 5 y = 7
y = 3 x + 9
Hint: | Perform a substitution.
Substitute y = 3 x + 9 into the first equation:
{4 x + 5 (3 x + 9) = 7
y = 3 x + 9
Hint: | Expand the left hand side of the equation 4 x + 5 (3 x + 9) = 7.
4 x + 5 (3 x + 9) = (15 x + 45) + 4 x = 19 x + 45:
{19 x + 45 = 7
y = 3 x + 9
Hint: | Choose an equation and a variable to solve for.
In the first equation, look to solve for x:
{19 x + 45 = 7
y = 3 x + 9
Hint: | Isolate terms with x to the left hand side.
Subtract 45 from both sides:
{19 x = -38
y = 3 x + 9
Hint: | Solve for x.
Divide both sides by 19:
{x = -2
y = 3 x + 9
Hint: | Perform a back substitution.
Substitute x = -2 into the second equation:
Answer: {x = -2 , y = 3