Question
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