( 1g5 )^2+21g2-( 1g2)^2计算此题.

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(1g5)^2+21g2-(1g2)^2计算此题.(1g5)^2+21g2-(1g2)^2计算此题.(1g5)^2+21g2-(1g2)^2计算此题.(1g5)^2+21g2-(1g2)^2==(1g

( 1g5 )^2+21g2-( 1g2)^2计算此题.
( 1g5 )^2+21g2-( 1g2)^2
计算此题.

( 1g5 )^2+21g2-( 1g2)^2计算此题.
( 1g5 )^2+21g2-( 1g2)^2
==(1g5)^2-(1g2)^2+2lg2
=(lg5+lg2)(lg5-lg2)+2lg2
=lg5-lg2+2lg2
=lg5+lg2
=1