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  1. If a + b = 10 and ab = 21, then the value of (a – b)2 is
    1. 15
    2. 16
    3. 17
    4. 18
Correct Option: B

a + b = 10 ;
ab = 21
∴  (a – b)2 = (a + b)2 – 4ab
= (10)2 – 4 × 21
= 100 – 84 = 16


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