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sum-1-1-4-7-1-4-7-10-1-7-10-13-1-10-13-16-1-13-16-19-1-94-97-100-




Question Number 208738 by Tawa11 last updated on 22/Jun/24
sum:     (1/(1.4.7))   +  (1/(4.7.10))  +  (1/(7.10.13))  +  (1/(10.13.16))  +  (1/(13.16.19))  +  ...  +  (1/(94.97.100))
$$\mathrm{sum}: \\ $$$$\:\:\:\frac{\mathrm{1}}{\mathrm{1}.\mathrm{4}.\mathrm{7}}\:\:\:+\:\:\frac{\mathrm{1}}{\mathrm{4}.\mathrm{7}.\mathrm{10}}\:\:+\:\:\frac{\mathrm{1}}{\mathrm{7}.\mathrm{10}.\mathrm{13}}\:\:+\:\:\frac{\mathrm{1}}{\mathrm{10}.\mathrm{13}.\mathrm{16}}\:\:+\:\:\frac{\mathrm{1}}{\mathrm{13}.\mathrm{16}.\mathrm{19}}\:\:+\:\:…\:\:+\:\:\frac{\mathrm{1}}{\mathrm{94}.\mathrm{97}.\mathrm{100}} \\ $$
Answered by BaliramKumar last updated on 22/Jun/24
(1/6)[(1/(1×4)) − (1/(97×100))]             d= 7−1 = 10−4 = 6  (1/6)×(((97×25−1))/(97×100)) = (1/6)×((2424)/(9700))    ((404)/(9700)) = ((101)/(2425))
$$\frac{\mathrm{1}}{\mathrm{6}}\left[\frac{\mathrm{1}}{\mathrm{1}×\mathrm{4}}\:−\:\frac{\mathrm{1}}{\mathrm{97}×\mathrm{100}}\right]\:\:\:\:\:\:\:\:\:\:\:\:\:\mathrm{d}=\:\mathrm{7}−\mathrm{1}\:=\:\mathrm{10}−\mathrm{4}\:=\:\mathrm{6} \\ $$$$\frac{\mathrm{1}}{\mathrm{6}}×\frac{\left(\mathrm{97}×\mathrm{25}−\mathrm{1}\right)}{\mathrm{97}×\mathrm{100}}\:=\:\frac{\mathrm{1}}{\mathrm{6}}×\frac{\mathrm{2424}}{\mathrm{9700}}\: \\ $$$$\:\frac{\mathrm{404}}{\mathrm{9700}}\:=\:\frac{\mathrm{101}}{\mathrm{2425}} \\ $$
Commented by Tawa11 last updated on 22/Jun/24
Thanks sir.
$$\mathrm{Thanks}\:\mathrm{sir}. \\ $$

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