(x(x+1))/2 = 3 Solve For x.
Multiply both sides by 2 ( (x(x + 1) ) = 6 )Multiply out the brackets ( x2 + x = 6 )Bring the 6 across ( x2 + x - 6 = 0 )Either using the quadratic formula or spotting the factors solve for x ( x = -3 or x = 2 )
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