Given x + y = 10, find the value of [(x + y) ^ 2 - (X-Y) ^ 2-2y (X-Y)] / 5Y
[(x+y)²-(x-y)²-2y(x-y)]÷5y
=[X²+2XY+Y²-X²+2XY-Y²-2XY+2Y²]÷5Y
=[2Y(X+Y)]÷5Y
=2/5(X+Y)
=2/5(10)
=4
Given x + 2Y + 3Y = 20, x + 3Y + 5Y = 31, find the value of X + y + Z
It's x + 2Y + 3Z = 20, x + 3Y + 5Z = 31. Subtract the first one from the second equation to get y + 2Z = 11. Then subtract the first one to get the answer x + y + Z = 9
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