> 数学 >
先化简,再求值:(3x2-4x+5)(3x2+4x-5)-x2(9x2-16),其中x=
1
20
人气:408 ℃ 时间:2020-06-16 18:13:53
解答
(3x2-4x+5)(3x2+4x-5)-x2(9x2-16)
=[3x2-(4x-5)][3x2+(4x-5)]-9x4+16x2
=9x4-(4x-5)2-9x4+16x2
=9x4-16x2+40x-25-9x4+16x2
=40x-25
x=
1
20
时,原式=40×
1
20
-25=-23.
推荐
猜你喜欢
© 2024 79432.Com All Rights Reserved.
电脑版|手机版