先化简,再求值:3(a-1)2-(2a+1)(a-2),其中a=−3/4.
先化简,再求值:3(a-1)
2-(2a+1)(a-2),其中a=
−.
数学人气:495 ℃时间:2020-05-01 20:12:43
优质解答
3(a-1)
2-(2a+1)(a-2)
=3(a
2-2a+1)-(2a
2-4a+a-2)
=3a
2-6a+3-2a
2+3a+2
=a
2-3a+5,
当a=-
时,原式=(-
)
2-3×(-
)+5=
+
+5=
.
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