4/1+4平方/1+4立方/1+4n次方/1

4平方带动五千瓦没问题,建议还是用6平方,可以满足日常所需,电线号小可引发火灾!

(1方+2方)/1*2 + (2方+3方)/2*3 +( 3方+4方)/3*4 + .+ (2011方+2012方)/2011*2012
是这样吗

(1+3)²-1²＝3×5,
(2+3)²-2²＝3×7,
(3+3)²-3²＝3×9,
(3+4)²-4²＝3×11,
… …
(n+3)²-n²＝(n²+6n+9)-n²＝3×(2n+3).

1/4+1/4²+1/4³+...+1/4^n
=(1/4)*[1-(1/4)^n]/(1-1/4)
=(1-1/4^n)/3
如果不懂,祝学习愉快!

(sin^4 α-cos^4 α+2cos^2 α)*tanα*cotα
=[(sin^2 α+cos^2 α))(sin^2 α-cos^2 α)+2cos^2 α]*[tanα*(1/tanα)]
=[1*(sin^2 α-cos^2 α)+2cos^2 α]*1
=sin^2 α-cos^2 α+2cos^2 α
=sin^2 α+cos^2 α
=1

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