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Question: If the equation ax<sup>2</sup> + 2bx – 3c = 0 have no real roots and 4 (a + b) \> 3c then...

If the equation ax2 + 2bx – 3c = 0 have no real roots and

4 (a + b) > 3c then

A

c < 0

B

c > 0

C

c ³ 0

D

c = 0

Answer

c < 0

Explanation

Solution

ax2 + 2bx – 3c = 0 has no real roots

Ž D < 0

Ž 4b2 + 12ac < 0 Ž b2 + 3ac < 0

Also 4 (a + b) > 3c

Ž 4a + 4b – 3 > 0 Ž f(2) > 0

Q D < 0 then ax2 + 2bx – 3c is either positive or negative " x ĪR according to a > 0 or a < 0 but f(2) > 0,

\ f(x) > 0 " x Ī R

So a > 0

Also f (0) > 0 Ž –3c > 0 Ž c < 0