21. यदि एक AP के पाँच पद का पाँच गुना उसके सातवें पद के सात गुना के बराबर हो, तो दर्शाइए कि बारहवाँ पद शून्य होगा।
In an A.P, if five times the fifth term is equal to seven times the seventh term, then show that twelfth term is
Zero.
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Step-by-step explanation:
5*A(5) = 7* A(7)
5{a+4d} = 7{a+6d}
5a + 20d = 7a + 42d
2a + 22d = 0
2(a+11d) = 0
a + 11d = 0
अर्थात A(12) = 0
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