Answers
(x-4)(x+1)×2
↓(x-4)(x+1)を先に計算
=(x^2-3x-4)×2
=2x^2-6x-8
2x^2-6x-8=72
2x^2-6x-80=0
2(x^2-3x-40)=0
↓2で両辺を割ると、
x^2-3x-40=0
(x-8)(x+5)=0
x=8,-5
ありがとうございます！
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