Some Special Series — MATHS STD 11 Science — Question
Rajasthan BoardEnglish MediumSTD 11 ScienceMATHSSome Special Series1 Mark
Question
Write the 50th term of the series 2 + 3 + 6 + 11 + 18 + ....
✓
Answer
We have, a1 = 2, a2 = 3 = 2 + 1, a3 = 6 = 2 + 1 + 3, a4 = 11 = 2 + 1 + 3 + 5, ............................. ............................. .............................. a50 = 2 + 1 + 3 + 5 + .... (50 terms) $=2+\frac{49}{2}\big[2\times1+(49-1)\times2\big]$ (As, the terms apart 2 are in A.P. with a = 1 and d = 2) $=2+\frac{49}{2}(2+48\times2)$ $=2+\frac{49}{2}\times98$ $=2+49^2$ $=2+2401$ $=2403$ So, the 50th term of the given series is 2403
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