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IF a,b,c are real numbers and 3b^2-8ac<0,then the equation ax^4+bx^3+cx^2+5x+7=0 cannot have all roots real. prove this.
The wording of the question is a dead giveaway. Suppose all the roots r1, r2, r3 and r4 are real, then we must have so that Now, from Vieta's formulas, . So, if all roots are real, we must necessarily have or . Since we are given that it implies that all roots cannot be real.
The wording of the question is a dead giveaway.
Suppose all the roots r1, r2, r3 and r4 are real, then we must have
so that
Now, from Vieta's formulas, . So, if all roots are real, we must necessarily have
or .
Since we are given that it implies that all roots cannot be real.
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