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Grade:
        
If the equation ax^2 +bx + 6 = 0 has real roots where a b are elements of R then the greatest value of 3a+b is 
a)4
b)-1
c)-2
d) 1
one year ago

Answers : (4)

Vasudeva Bhat
14 Points
							
Take x=3,
=>f(3)≥0
=>9a+3b+6≥0
=>3a+b≥-2
Hence, we can get 3a+b=-2 as the minimum value.
 
 
 
 
Thanks
 
 
 
 
Cheers.
 
 
one year ago
Meghendra Agrawal
8 Points
							
Please tell why can’t f(3) Please give the answer soon. or
one year ago
Meghendra Agrawal
8 Points
							
Why can’t f(3) be less than 0?? Can we also assume x = 1 or 2 or – 1 but how will we determine whether f(x) would be greater than or less than 0??
one year ago
Vasudeva Bhat
14 Points
							
I checked with the notes my sir had provided and I realised the question you've given needs to be corrected. In the actual question, there are no real roots. So The line won't intersect x axis at all that means ax^2+bx+c>0
We substitute x=3 because we need to get 3a+b and one of the ways we can obtain it is by substituting 3 and we get 3a+b>-2
I hope your doubt would have been cleared by now.
 
Thanks
 
Cheers!
one year ago
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