Core 1 discriminant and quadraticinequalties AS Maths help Watch

wednesday_adams
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#1
Report Thread starter 4 years ago
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Can anyone tell me if I'm approaching this maths problem in the right way?

It says:

Find the range of values of b for9x^2 +bx+4=0 to have 2 real distinct roots.

So I said:
a=9
b=b
c=4

then because theres 2 distinct roots i said: b^2-4ac>0


b^2-4x9x4>0

b^2-144>0
then i factored it so = (b-12)(b+12)>0

But then I don't know what the answer is.
Is it b=-12 or b=12 as the answer?

Please let me know if I'm doing this completely wrong.

Instead of factoring it should I have done

b^2-144>0 (add 144 to both sides)
b^2>144
b>12?

??? I'm so confused.
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BBeyond
Badges: 5
#2
Report 4 years ago
#2
(Original post by wednesday_adams)
Can anyone tell me if I'm approaching this maths problem in the right way?

It says:

Find the range of values of b for9x^2 +bx+4=0 to have 2 real distinct roots.

So I said:
a=9
b=b
c=4

then because theres 2 distinct roots i said: b^2-4ac>0


b^2-4x9x4>0

b^2-144>0
then i factored it so = (b-12)(b+12)>0

But then I don't know what the answer is.
Is it b=-12 or b=12 as the answer?

Please let me know if I'm doing this completely wrong.

Instead of factoring it should I have done

b^2-144>0 (add 144 to both sides)
b^2>144
b>12?

??? I'm so confused.
Draw the graph of b^2 - 144 - you want to find the bits which are greater than 0 on the graph.

Your last bit is right apart from the fact it would be + or - 12 rather than just + 12 (as when you square root something it can be positive or negative)
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