Toán Lớp 8: (-x^2 + 3x +4) làm thế nào để ra (-x -1).(4-x) vậy ?
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Toán Lớp 8: (-x^2 + 3x +4) làm thế nào để ra (-x -1).(4-x) vậy ?
Comments ( 2 )
-x^2 +3x+4
=-(x^2 -3x-4)
=-(x^2 +x -4x -4)
=-[(x^2 +x) -(4x +4)]
=-[(x.(x+1) – 4.(x+1)]
=-(x+1).(x-4)
=(-x-1).(x-4)
Giải đáp:
-x^2 + 3x +4
=-(x^2−3x−4)
=−(x^2+x−4x−4)
=−[x(x+1)−4(x+1)]
=−(x+1)(x-4)
=(-x-1)(x-4)