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-13*x-26 = (1/2)*u // - (1/2)*u
-((1/2)*u)-13*x-26 = 0
(-1/2)*u-13*x-26 = 0
-1/2*u-13*x-26 = 0 // + -1/2*u-26
-13*x = -(-1/2*u-26) // : -13
x = (-(-1/2*u-26))/(-13)
x = (26-(-1/2*u))/(-13)
x = (26-(-1/2*u))/(-13)
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