m^2 -11m -60 = 0
m^2 -11m =60
(m^2 -11m + 121/4) = 361/4
(m - 11/2)^2 = 361/4
m - 11/2 = + or - 19/2
m = 11/2 + 19/2, 11/2 - 19/2
m = 15, -4
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m^2 -11m -60
(11 +- Square root (121 +240))/2
11/2 +- 19/2
m= 15, -4
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m^2 -11m -60
(m - 15) (m + 4)
m = 15, -4
