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JEE Main 20211 SeptemberEvening Shift
Exam
JEE Main
Year
2021
Date
1 September
Shift
Evening Shift
Subject
Mathematics
Chapter
Complex Number

JEE Main 2021 · 1 September · Evening Shift · Mathematics · Complex Number

If for the complex numbers z satisfying | z - 2 - 2i | ≤ 1 , the...

If for the complex numberszz satisfying ∣z−2−2i∣≤1| z - 2 - 2i | \le 1, the maximum value of ∣3iz+6∣| 3iz + 6 | is attained at a+iba + ib, then a+ba + b is equal to _____ .If for the complex numbers z satisfying | z - 2 - 2i | ≤ 1 , the maximum value of | 3iz + 6 | is attained at a + ib ,

Correct answer

0

Step-by-step solution

Given that: ∣z−2−2i∣≤1| z - 2 - 2i | \le 1 which represents a circle with centre at (2,2)andradius( 2, 2 ) and radius= 1.</p><p>Now.</p><p>Now| 3iz + 6 | = | 3i ( z - 2i ) | = | 3i | | z - 2i |</p><p>Asweknowthat,[∣z1z2∣=∣z1∣∣z2∣]</p><p>As we know that, \left[| {z}_{1}{z}_{2} | = | {z}_{1} | | {z}_{2} |\right]

From tha diagram we can see that, ∣3iz+6∣=3∣z−2i∣| 3iz + 6 | = 3 | z - 2i | is maximum at z=3+2iz = 3 + 2i because a point on the circle, which has maximum distance from (0,2)( 0, 2 ) is (3,2)( 3, 2 ).

If for the complex numbers z satisfying | z - 2 - 2i | ≤ 1 , the maximum value of | 3iz + 6 | is attained at a + ib ,

So, a=3 and  a = 3 \text{\text{ and } } b = 2

⇒a+b=5⇒ a + b = 5

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