问条对数计算题(lg 2)^2+lg 5*lg 20 -1=?

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问条对数计算题(lg 2)^2+lg 5*lg 20 -1=?
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问条对数计算题(lg 2)^2+lg 5*lg 20 -1=?
问条对数计算题
(lg 2)^2+lg 5*lg 20 -1=?

问条对数计算题(lg 2)^2+lg 5*lg 20 -1=?
(lg 2)^2+lg 5*lg 20 -1
=(lg 2)^2+lg 5*lg (4*5)-1
=(lg 2)^2+lg 5*(lg 4+lg5)-1
=(lg 2)^2+lg 5*(2lg2+lg5)-1
=(lg 2)^2+lg 5*2lg2+lg5*lg5-1
=(lg2+lg5)^2-1
=1-1
=0

原式=(lg 2)^2+lg5×(lg4+lg5)-1
=(lg 2)²+(lg5)²+2lg2×lg5-1(lg4=2lg2)
=(lg2+lg5)²-1) (逆用完全平方公式)
=1-1=0

由lg5*lg20=lg5*(lg4+lg5)=(lg5)^2+2*lg2*lg5
原式=(lg2)^2+(lg5)^2+2*lg2*lg5-1
=(lg2+lg5)^2-1
=0

(lg 2)^2+lg 5*lg 20 -1
=(lg 2)^2+(1-lg 2)*lg 20 -1
=(lg2)^2+(1-lg2)(1+lg2)-1
=(lg 2)^2+1-(lg2)^2-1
=0