If 2x² – 2y = 125 and x - y = 2.5, find the value of
x + y

We can solve this using substitution.

because x-y=2.5

x=y+2.5

Now substitute x into other equation.

2(y+2.5)^2-2y=125

2y^2+10y+12.5-2y=125

2y^2+8y-112.5=0

Now comes the ugly part

y=-4+-sqrt(16+900)

y=-4+-sqrt916

y=-4+-2sqrt229

x=-1.5+-2sqrt229

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