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If |a|=|b|=1 and |a+b|=sqrt(3), then the value of (3a-4b).(2a+5b) is |
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Answer» `-21` `RARR""a*b=(3-1-1)/2=1/2"...(i)"[because|a|=|b|=1, "GIVEN"]` `:.""(3a-4b)*(2a+5b)=6|a|^2+15a*b-20|b|^2` `=6+7a*b-20` `=6+7/2-20"[from Eq. (i)]"` `=(7-28)/2-21/2` |
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