1.

ABC is a right-angled triangle in which angleB=90^(@) and BC=a. If n points L_(1),L_(2),…,L_(n) on AB is divided in n+1 equal parts and L_(1)M_(1), L_(2)M_(2),…,L_(n)M_(n) are line segments paralllel to BC and M_(1), M_(2),….,M_(n) are on AC, then the sum of the lengths of L_(1)M_(1), L_(2)M_(2),...,L_(n)M_(n) is

Answer»

`(a(N+1))/(2)`
`(a(n-1))/(2)`
`(an)/(2)`
none of these

Solution :`(AL_(1))/(AB)=(L_(1)M_(1))/(BC)`
`=1/(n+1)=(L_(1)M_(1))/a`
`(AL_(2))/(AB)=(L_(2)M_(2))/(BC)`
`rArr2/(n+1)=(L_(2)M_(2))/a`
`rArrL_(2)M^(2)=(2a)/(n+1), ETC`
HENCE. The required sum is
`a/(n+1)+(2a)/(n+1)+(3a)/(n+1)+….+(na)/(n+1)`
`=a/(n+1)(n(n+1))/2`
`=(an)/2`


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