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a in (-oo:+oo)
3/4-(4*a) = -13/4 // + -13/4
3/4-(4*a)-(-13/4) = 0
3/4-4*a+13/4 = 0
4-4*a = 0 // - 4
-4*a = -4 // : -4
a = -4/(-4)
a = 1
a = 1
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