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If (a_n=n^3-1) then which term is equal to (124)?यदि (a_n=n^3-1) है तो कौन-सा पद (124) के बराबर होगा?
Answer and explanationउत्तर और व्याख्या
Correct answer:सही उत्तर: \(a_5\)\(a_5\)
Given \(a_n=n^3-1\), set \(a_n=124\). Then \(n^3-1=124\), so \(n^3=125=5^3\). Hence \(n=5\), and therefore \(a_5=124\). The close distractor \(a_4\) is incorrect because \(a_4=63\). Exam tip: for expressions of the form \(n^3-1\), add 1 first and identify the perfect cube.दिया है \(a_n=n^3-1\)। \(a_n=124\) रखने पर \(n^3-1=124\), अतः \(n^3=125=5^3\)। इसलिए \(n=5\) और \(a_5=124\) होगा। \(a_4=63\) होता है, इसलिए वह निकट का लेकिन गलत विकल्प है। परीक्षा टिप: \(n^3-1\) वाले प्रश्न में पहले 1 जोड़कर पूर्ण घन पहचानें।
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