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If veca+vecb+vecc = vec0, |veca| = 3 , |vecb| = 5 and |vecc| = 7, find the angle between veca and vecb. |
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Answer» SOLUTION :`veca+vecb+VECC` = 0 `implies veca+vecb` = `-vecc` `implies (veca+vecb)^2` = `(-vecc)^2 `implies |veca|^2+|vecb|^2+2veca.vecb` = `|vecc|^2` `implies 9+25+2veca.vecb` = 49 `implies 2veca.vecb` = 49-34 = 15 `implies 2|veca||vecb|COSTHETA` = 15 (where `theta` is the ANGLE between `veca` and `vecb`) `implies costheta` = 15/(2.3.5) = 1/2 `implies theta` = `pi/3` |
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