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次数の低いbについて降べきの順にします。
(与式)
= b(a²-1)+a-1
= b(a+1)(a-1)+(a-1)
= (a-1){b(a+1)+1}
= (a-1)(ab+b+1)
となります。
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次数の低いbについて降べきの順にします。
(与式)
= b(a²-1)+a-1
= b(a+1)(a-1)+(a-1)
= (a-1){b(a+1)+1}
= (a-1)(ab+b+1)
となります。
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are also looking at these questions 😉
b(a+1)(a-1)+(a-1)
= (a-1){b(a+1)+1}
の部分は、共通因数 a-1 でくくっています。