there is____but a piese of paper in the box.A something B anything C nothing D someone

there is____but a piese of paper in the box.A something B anything C nothing D someone LIAO PI A A 化简间sin（a-2pi)cos(a+pi）tan(a-99pi)cos(pi-a)sin(3pi-a)sin（-a-pi） 英语翻译A sigma is formed when there is end-on overlap of atomic orbitals.A pi is formed when there is sideways overlap of atomic orbitals. pi pi cos(a-pi/2)/sin(5pi/2加a)×sin(a-2pi)×cos(2pi-a) 哪个 pi a nei 呜呜 csc(a+pi/2)=? sec(a-pi/2)=? sec(a+pi/2)=? sin(PI/2+a)=-4/5 a属于(Pi,3pi/2)则cos(Pi/3-a)为 cos(Pi+a)=-0.5,3/2Pi cos(a-pi/3)=12/13,pi/3 解方程：sin(2*a)/pi+(pi-a)/pi=0.8,最好能给出matlab程序. 化简(高一)[sin^2(pi+a)cos(pi+a)]/[tan(pi+a)cos^3(-pi-a)tan(2pi+a)] tana=2求sin(pi-a)cos(2pi-a)sin(-a+3pi/2)/tan(-a-pi)sin(-pi-a) f(a)=sin(pi-a)cos(2pi-a)tan(-a+3pi/2)/cos(-pi-a) 求 f(-31pi/3)的值