已知一维晶体的电子能带可写成:(k)=dfrac ({h)^2}(m{a)^2}(dfrac (7)(8)-cos ka+dfrac (1)(8)cos 2ka,式中a是晶格常数。试求:(1)能带的宽度(2)电子在波矢k的状态时的速度(3)能带底部和顶部电子的有效质量

1、设有一维晶体的电子能带可写成(k)=dfrac ({h)^2}(m{a)^2}(dfrac (7)(8)-cos ka+dfrac (1)(8)cos 2k

cos dfrac (x)({2)^n})（提示：lim _(xarrow infty )(cos dfrac (x)(2)cos dfrac (x)(4)co

已知曲线积分(int )_(1)^1(1+dfrac ({cos )^2}({x)^2}cos dfrac (y)(x))dx+(sin dfrac (y)(x

已知一维单原子晶格的格波色散关系为:(omega )^2(q)=dfrac (2beta )(M)(1-cos qa),试求:(1)格波的模密度(omega )

(sin x)=dfrac (1)({cos )^2x} in (0,dfrac (pi )(2)),则(sin x)=dfrac (1)({cos )^2x}

关于函数=cos x-dfrac (1)(2)cos 2x的极值结论错误的是( ).A 极大值=cos x-dfrac (1)(2)cos 2xB 极小值=co

(int )_(-dfrac {pi )(2)}^dfrac (pi {2)}((cos )^2x+dfrac (xcos x)(1+{cos )^2x})dx

(3) (int )_(0)^dfrac (pi {4)}dfrac (x)(1+cos 2x)dx= () .-|||-(A) dfrac (pi )(8)+

2.求极限lim _(xarrow 0)(dfrac (1)(xsin x)-dfrac (cos x)({x)^2}) ()2.求极限

[题目]求 lim _(xarrow infty )((sin dfrac {2)(x)+cos dfrac (1)(x))}^x