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Q. `|(x+y,x,x),(15x+4y,4x,2x),(10x +8y,8x,3x)|=x^3` |
Answer» Let the given determinant be `Delta`. Then, `Delta = |{:(x+y, x, x),(5x+4y,4x, 2x),(10x+8y, 8x, 3x):}|` `= |{:(x+y, x, x),(3x+2y, 2x, 0),(7x+5y, 5x, 0):}| [R_(2) to (R_(2)-2R_(1)) " and"R_(3)to(R_(3)to 3R_(1))]` `=x* |{:(3x+2y, 2x),(7x+5y, 5):}| ["expanded by"C_(3)]` `=x^(2)* |{:(3x+2y, 2x),(7x+5y, 5):}| ["taking x common from "C_(2)]` `=x^(2) *[5(3x +2y)-2(7x+5y)] =(x^(2)*x) =x^(3).` Hence, `Delta = x^(3)` |
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