Find the sum of the first n terms of 4+44+444+....
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=4(1+11+111+1111+−−−−−−nterms)
=49(9+99+999+−−−−−−−−−−−nterms)
=49(10−1+100−1+1000−1+−−−−−−−−−−−nterms)
=49((10−1)+(102−1)+(103−1)+−−−−−−−−−−−nterms)
=49[10+102+103+−−−−−−−−−−−nterms−n]
=49[10(10n−1)10−1−n]
=49[10(10n−1)9−n].
=49(9+99+999+−−−−−−−−−−−nterms)
=49(10−1+100−1+1000−1+−−−−−−−−−−−nterms)
=49((10−1)+(102−1)+(103−1)+−−−−−−−−−−−nterms)
=49[10+102+103+−−−−−−−−−−−nterms−n]
=49[10(10n−1)10−1−n]
=49[10(10n−1)9−n].
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