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NCERT Class XI Mathematics - Complex Numbers and Quadratic Equations - Solutions

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Question : 25 of 52
Marks: +1, -0
x2x^2 + 3x + 9 = 0
Solution:  
We have, x2x^2 + 3x + 9 = 0
Comparing the given equation with the general form ax2ax^2 + bx + c = 0,
we get a = 1, b = 3, c = 9
∴ x = b±b24ac2a\frac{-b\pm\sqrt{b^2-4ac}}{2a} = 3±(3)24×1×92.1\frac{-3\pm\sqrt{(3)^2-4\times1\times9}}{2.1} = 3±9362\frac{-3\pm\sqrt{9-36}}{2}
= 3±272\frac{-3\pm\sqrt{-27}}{2} = 3±332\frac{-3\pm3\sqrt{-3}}{2} = 3±i(33)2\frac{-3\pm i(3\sqrt{3})}{2}
∴ The roots of the given equation are 3+i(33)2\frac{-3+i(3\sqrt{3})}{2} and 3i(33)2\frac{-3-i(3\sqrt{3})}{2}
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