Question 270497: Please explain this linear equation:
If x + y = 15 and x -y = -19 then xy = ?
Thanks,
Jesse Evans
jesseevans@hughes.net
Found 3 solutions by vleith, persian52, Alan3354:
Answer by vleith(2983)   (Show Source):
Answer by persian52(161)  (Show Source):
You can put this solution on YOUR website! i think you meant like this?
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x+y=15_x-y=-19
Since y does not contain the variable to solve for, move it to the right-hand side of the equation by subtracting y from both sides.
x=-y+15_x-y=-19
Replace all occurrences of x with the solution found by solving the last equation for x. In this case, the value substituted is -y+15.
x=-y+15_(-y+15)-y=-19
Remove the parentheses around the expression -y+15.
x=-y+15_-y+15-y=-19
Since -y and -y are like terms, subtract y from -y to get -2y.
x=-y+15_-2y+15=-19
Since 15 does not contain the variable to solve for, move it to the right-hand side of the equation by subtracting 15 from both sides.
x=-y+15_-2y=-15-19
Subtract 19 from -15 to get -34.
x=-y+15_-2y=-34
Divide each term in the equation by -2.
x=-y+15_-(2y)/(-2)=-(34)/(-2)
Simplify the left-hand side of the equation by canceling the common terms.
x=-y+15_y=-(34)/(-2)
Simplify the right-hand side of the equation by simplifying each term.
x=-y+15_y=17
Replace all occurrences of y with the solution found by solving the last equation for y. In this case, the value substituted is 17.
x=-(17)+15_y=17
Multiply -1 by the 17 inside the parentheses.
x=-17+15_y=17
Add 15 to -17 to get -2.
x=-2_y=17
This is the solution to the system of equations.
Answer: x=-2
Answer: y=17
Answer by Alan3354(69443)  (Show Source):
You can put this solution on YOUR website! x = -2
y = 17
xy = -34
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The other tutors worked it, but slipped up at the end.
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I agree, do not give your name and email. First names are ok, but be cautious.
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