已知f1(x)=e^xsinx,fn(x)= fn-1'(x),n≥2,求f1(0)+f2(0)+f3(0)+ ……f2011(0)的值
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已知f1(x)=e^xsinx,fn(x)= fn-1'(x),n≥2,求f1(0)+f2(0)+f3(0)+ ……f2011(0)的值
已知f1(x)=e^xsinx,fn(x)= fn-1'(x),n≥2,求f1(0)+f2(0)+f3(0)+ ……f2011(0)的值
已知f1(x)=e^xsinx,fn(x)= fn-1'(x),n≥2,求f1(0)+f2(0)+f3(0)+ ……f2011(0)的值
f1(x)=e^xsinx f1(0)=0
f2(x)=f1'(x)=(e^xsinx)'=e^x(sinx+cosx) f2(0)=1
f3(x)=[e^x(sinx+cosx)]'=2e^xcosx f3(0)=2
f4(x)=(2e^xcosx)'=2e^x(cosx-sinx) f4(0)=2
f5(x)=-4e^xsinx f5(0)=0
f6(x)=f5'(x)=(-4e^xsinx)'=-4e^x(sinx+cosx),f6(0)=-4f2(0)
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每四项和,成等比数列,且公比为-4
前四项的和为5,再下面为-20,80,.
2011/4=502.3,第502项为-20*(-4)^(501),
第503项为5*(-4)^(502),但最后只有3项和为5*(-4)^(502)*3/5=3*(-4)^(502),
f1(0)+f2(0)+f3(0)+ ……f2011(0)=5(1-(-4)^(502))/(1-(-4))+3*(-4)^(502),
=4^502-1+3*4^502=4^503-1.
f1 ' (x) = e^x (sinx + cosx) = √2 e^x (sin(x+π/4)
f2(x) = √2 e^x (sin(x+π/4)
fn(x) = (√2)^(n-1) e^x sin【x+(n-1)π/4 】
f1(0)+f2(0)+f3(0)+ ……f2011(0)
= 【0 + √2 sin (π/4) + 2 sin(π/2) + ...
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f1 ' (x) = e^x (sinx + cosx) = √2 e^x (sin(x+π/4)
f2(x) = √2 e^x (sin(x+π/4)
fn(x) = (√2)^(n-1) e^x sin【x+(n-1)π/4 】
f1(0)+f2(0)+f3(0)+ ……f2011(0)
= 【0 + √2 sin (π/4) + 2 sin(π/2) + (√2)^3 sin (3π/4) + 0
+ (√2)^5 sin (5π/4) +(√2)^6 sin (6π/4) + (√2)^7 sin (7π/4) 】
+ 【(√2)^8 sin (2π) + ...... 】+ 0 + (√2)^2009 sin (2009π/4) + (√2)^2010 sin (2010π/4)
= (-15) [ 1 + 16 + 16^2 + ......+ 16^250 ] + 2^1004 + 2^1005
= ( 1 - 16^251) + 2^1004 + 2^1005
=2^1005+1
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