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Question
Solve the following quadratic equation by completing square: z2 + 4z - 7 = 0.
Solution
The given quadratic equation is
z2 + 4z - 7 = 0
∴ z2 + 4z = 7 ....eq (i)
Third term =`(1/2 "coefficient of z")^2`
`=[1/2 (4)]^2 = 2^2 = 4`
Adding 4 in eq (i) on both the sides
z2 + 4z + 4 = 7 + 4
(z + 2)2 = 11
∴ z + 2 = `+- sqrt11`
∴ z + 2 = `sqrt 11` OR z + 2 = `- sqrt11`
∴ z = `-2 + sqrt11` OR z =`-2-sqrt1`
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