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    				| 1. | यदि a2 + b2 + c2 = 20 व a + b+ c =0, तब ab+ bc + ca का मान ज्ञात कीजिए। | 
| Answer» (a + b + c = 0 ) वर्ग करने पर a2 + b2 + c2 + 2(ab + bc + ca) = 0 20 + 2(ab + bc + ca) = 0 2(ab + bc + ca) = 0 – 20 ab + bc + ca = -20/2 = -10 | |