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

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Question : 41 of 52
Marks: +1, -0
21x2−28x+10=021x^2-28x+10=0
Solution:  
We have , 21x2−28x+10=021x^2-28x+10=0
Comparing the given equation with the general form ax2ax^2 + bx + c = 0,
we get a = 21, b = – 28, c = 10
∴ x = −b±b2−4ac2a\frac{-b \pm \sqrt{b^2-4ac}}{2a} = 28±(−28)2−4×21×102×21\frac{28 \pm \sqrt{(-28)^2 - 4 \times 21 \times 10}}{2 \times 21}
= 28±784−84042\frac{28 \pm \sqrt{784-840}}{42} = 28±−5642\frac{28 \pm \sqrt{-56}}{42} = 14±−1421\frac{14 \pm \sqrt{-14}}{21} = 14±i1421\frac{14 \pm i\sqrt{14}}{21}
= 1421±i1421\frac{14}{21} \pm \frac{i\sqrt{14}}{21} = 23±i1421\frac{2}{3} \pm \frac{i\sqrt{14}}{21}
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