09实验三及答案.docx
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09实验三及答案
实验三、
1、设x为符号变量,令y=x4+2x2+1,z=y2,w=sin(z),试求w关于x的符号表达式,并求当x=5时,w的小数点之后具有1位、2位、10位、20位和50位有效数字的数值解。
解:
>>symsx
>>y=x^4+2*x^2+1
y=
x^4+2*x^2+1
>>z=y^2
z=
(x^4+2*x^2+1)^2
>>w=sin(z)
w=
sin((x^4+2*x^2+1)^2)
>>u=subs(w,5)
u=
-0.0673
>>vpa(u,1)
ans=
-.7e-1
>>vpa(u,2)
ans=
-.67e-1
>>vpa(u,10)
ans=
-.6734017262e-1
>>vpa(u,20)
ans=
-.67340172619870686255e-1
>>vpa(u,50)
ans=
-.67340172619870686254728298081317916512489318847656e-1
2、求级数
的级数和以及级数
的级数和。
解:
>>symsnk
>>r1=symsum((-1)^(n-1)/(n*(n+1)),n,1,inf)
r1=
-1+2*log
(2)
>>r2=symsum((-1)^(n-1)/((2*n+1)*(2*n+3)),n,0,inf)
r2=
1/2-1/4*pi
3、将二元函数
展开为x的4阶、y的7阶麦克劳林级数,在x=3处展开为6阶泰勒级数。
>>symsxy
>>z=sin(2*x+5*y^2)
z=
sin(2*x+5*y^2)
>>taylor(z,5,x)
ans=
sin(5*y^2)+2*cos(5*y^2)*x-2*sin(5*y^2)*x^2-4/3*cos(5*y^2)*x^3+2/3*sin(5*y^2)*x^4
>>taylor(z,8,y)
ans=
sin(2*x)+5*cos(2*x)*y^2-25/2*sin(2*x)*y^4-125/6*cos(2*x)*y^6
>>taylor(z,7,x,3)
ans=
sin(6+5*y^2)+2*cos(6+5*y^2)*(x-3)-2*sin(6+5*y^2)*(x-3)^2-4/3*cos(6+5*y^2)*(x-3)^3+2/3*sin(6+5*y^2)*(x-3)^4+4/15*cos(6+5*y^2)*(x-3)^5-4/45*sin(6+5*y^2)*(x-3)^6
4、对符号表达式
,分别进行如下变换。
(1)关于y的Fourier变换及其逆变换。
(2)关于x的Laplace变换及其逆变换。
(3)分别关于x和y的Z变换及其逆变换。
解:
>>symsxy
>>symsxyuvw
>>z=(2*x+3*y)*exp(-2*x^2-3*y^2)
z=
(2*x+3*y)*exp(-2*x^2-3*y^2)
>>fourier(z,y,u)
ans=
1/6*exp(-2*x^2)*3^(1/2)*exp(-1/12*u^2)*pi^(1/2)*(4*x-i*u)
>>ifourier(z,y,u)
ans=
1/12*3^(1/2)/pi^(1/2)*(4*x+i*u)*exp(-2*x^2-1/12*u^2)
>>laplace(z,x,u)
ans=
1/2*exp(-3*y^2)-1/8*erfc(1/4*u*2^(1/2))*exp(-3*y^2+1/8*u^2)*2^(1/2)*pi^(1/2)*(u-6*y)
>>ilaplace(z,x,u)
ans=
2*ilaplace(exp(-2*x^2-3*y^2)*x,x,u)+3*y*ilaplace(exp(-2*x^2-3*y^2),x,u)
>>ztrans(z,x,u)
ans=
-2*u*diff(ztrans(exp(-2*x^2-3*y^2),x,u),u)+3*y*ztrans(exp(-2*x^2-3*y^2),x,u)
>>iztrans(z,x,u)
ans=
iztrans((2*x+3*y)*exp(-2*x^2-3*y^2),x,u)
>>ztrans(z,y,u)
ans=
2*x*ztrans(exp(-2*x^2-3*y^2),y,u)-3*u*diff(ztrans(exp(-2*x^2-3*y^2),y,u),u)
>>iztrans(z,y,u)
ans=
iztrans((2*x+3*y)*exp(-2*x^2-3*y^2),y,u)
5、求解方程组
解:
>>[x,y,z]=solve('2*x-3*y-7','x^3-4*x^2*y^2+4*y-3*z','x^2-3*y^2*z+4*z')
x=
2
5.2762369469878861276035537442151+.34604224719617823521718689597631*i
-.617992195679576766250682175601e-1+.63499917504638615341506346339221*i
2.133********01430980430289466902
-.617992195679576766250682175601e-1-.63499917504638615341506346339221*i
5.2762369469878861276035537442151-.34604224719617823521718689597631*i
y=
-1
1.1841579646585907517357024961434+.23069483146411882347812459731754*i
-2.3745328130453051177500454783734+.42333278336425743561004230892814*i
-.91091696989323793463798070220653
-2.3745328130453051177500454783734-.42333278336425743561004230892814*i
1.1841579646585907517357024961434-.23069483146411882347812459731754*i
z=
-4
2.7108479891516480785507291108309-16.833546096768767917471752231306*i
-.23579864163827571542863885103e-1-.17830800457391690511849863412e-1*i
-3.0134251388645299029046193403398
-.23579864163827571542863885103e-1+.17830800457391690511849863412e-1*i
2.7108479891516480785507291108309+16.833546096768767917471752231306*i
6、求解微分方程组
在无初始条件和有初始条件
时的解。
解:
>>[x,y]=dsolve('D2x+Dy+3*x=2*t*sin(t)','D2y-4*Dx+3*y=3*t*cos(t)','t')
x=
11/64*t*sin(t)-7/32*cos(t)*t^2+39/256*cos(t)+C1*sin(t)+C2*cos(t)+C3*sin(3*t)+C4*cos(3*t)
y=
3/32*t*cos(t)+7/16*sin(t)*t^2-39/128*sin(t)+2*C1*cos(t)-2*C2*sin(t)-2*C3*cos(3*t)+2*C4*sin(3*t)
>>[x,y]=dsolve('D2x+Dy+3*x=2*t*sin(t)','D2y-4*Dx+3*y=3*t*cos(t)','Dx
(2)=5','x
(2)=7','Dy
(2)=4','y
(2)=2','t')
x=
11/64*t*sin(t)-7/32*cos(t)*t^2+31/256*cos(t)+1/64*(-8*sin
(2)*cos
(2)+49*cos
(2)^2+304*cos
(2)-128*sin
(2)+51*sin
(2)^2)/(sin
(2)^2+cos
(2)^2)*cos(t)-1/32*(2*sin
(2)^2+sin
(2)*cos
(2)-152*sin
(2)-2*cos
(2)^2-64*cos
(2))/(sin
(2)^2+cos
(2)^2)*sin(t)-1/256/(cos(6)^2+sin(6)^2)*(-11*sin
(2)*sin(6)+72*sin
(2)*cos(6)+3*cos
(2)*cos(6)-576*cos(6)+40*cos
(2)*sin(6)+256*sin(6))*cos(3*t)-1/256*(72*sin
(2)*sin(6)+11*sin
(2)*cos(6)+3*cos
(2)*sin(6)-40*cos
(2)*cos(6)-576*sin(6)-256*cos(6))/(cos(6)^2+sin(6)^2)*sin(3*t)
y=
7/16*sin(t)*t^2-31/128*sin(t)+3/32*t*cos(t)-1/32*(-8*sin
(2)*cos
(2)+49*cos
(2)^2+304*cos
(2)-128*sin
(2)+51*sin
(2)^2)/(sin
(2)^2+cos
(2)^2)*sin(t)-1/16*(2*sin
(2)^2+sin
(2)*cos
(2)-152*sin
(2)-2*cos
(2)^2-64*cos
(2))/(sin
(2)^2+cos
(2)^2)*cos(t)-1/128/(cos(6)^2+sin(6)^2)*(-11*sin
(2)*sin(6)+72*sin
(2)*cos(6)+3*cos
(2)*cos(6)-576*cos(6)+40*cos
(2)*sin(6)+256*sin(6))*sin(3*t)+1/128*(72*sin
(2)*sin(6)+11*sin
(2)*cos(6)+3*cos
(2)*sin(6)-40*cos
(2)*cos(6)-576*sin(6)-256*cos(6))/(cos(6)^2+sin(6)^2)*cos(3*t)