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Let a, b, c and m in R^(+). The possible...

Let `a`, `b`, `c` and `m in R^(+)`. The possible value of `m` (independent of `a`, `b` and `c`) for which atleast one of the following equations have real roots is
`{:(ax^(2)+bx+cm=0),(bx^(2)+cx+am=0),(cx^(2)+ax+bm=0):}}`

A

`(1)/(2)`

B

`(1)/(8)`

C

`(1)/(12)`

D

`(1)/(4)`

Text Solution

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To solve the problem, we need to find the possible values of \( m \) such that at least one of the following quadratic equations has real roots: 1. \( ax^2 + bx + cm = 0 \) 2. \( bx^2 + cx + am = 0 \) 3. \( cx^2 + ax + bm = 0 \) ### Step 1: Understanding the Condition for Real Roots For a quadratic equation \( Ax^2 + Bx + C = 0 \) to have real roots, the discriminant \( D \) must be greater than or equal to zero: \[ D = B^2 - 4AC \geq 0 \] ### Step 2: Calculate the Discriminants Let's calculate the discriminants for each of the three equations. 1. For \( ax^2 + bx + cm = 0 \): \[ D_1 = b^2 - 4a(cm) = b^2 - 4acm \] 2. For \( bx^2 + cx + am = 0 \): \[ D_2 = c^2 - 4b(am) = c^2 - 4abm \] 3. For \( cx^2 + ax + bm = 0 \): \[ D_3 = a^2 - 4c(bm) = a^2 - 4cbm \] ### Step 3: Combine the Conditions We need at least one of these discriminants to be non-negative: \[ D_1 \geq 0 \quad \text{or} \quad D_2 \geq 0 \quad \text{or} \quad D_3 \geq 0 \] This leads us to the combined inequality: \[ (b^2 - 4acm) + (c^2 - 4abm) + (a^2 - 4cbm) \geq 0 \] Simplifying this gives: \[ a^2 + b^2 + c^2 - 4m(ab + ac + bc) \geq 0 \] ### Step 4: Rearranging the Inequality Rearranging the inequality, we have: \[ a^2 + b^2 + c^2 \geq 4m(ab + ac + bc) \] Dividing both sides by \( ab + ac + bc \) (which is positive since \( a, b, c > 0 \)): \[ \frac{a^2 + b^2 + c^2}{ab + ac + bc} \geq 4m \] ### Step 5: Finding the Minimum Value Using the Cauchy-Schwarz inequality, we know: \[ (a^2 + b^2 + c^2)(1 + 1 + 1) \geq (a + b + c)^2 \] This implies: \[ a^2 + b^2 + c^2 \geq \frac{(a + b + c)^2}{3} \] Thus, we can conclude: \[ \frac{a^2 + b^2 + c^2}{ab + ac + bc} \geq 1 \] This means: \[ 1 \geq 4m \quad \Rightarrow \quad m \leq \frac{1}{4} \] ### Step 6: Considering the Positive Real Numbers Since \( m \) is a positive real number, we have: \[ 0 < m \leq \frac{1}{4} \] ### Final Answer The possible values of \( m \) are: \[ m \in (0, \frac{1}{4}] \]

To solve the problem, we need to find the possible values of \( m \) such that at least one of the following quadratic equations has real roots: 1. \( ax^2 + bx + cm = 0 \) 2. \( bx^2 + cx + am = 0 \) 3. \( cx^2 + ax + bm = 0 \) ### Step 1: Understanding the Condition for Real Roots For a quadratic equation \( Ax^2 + Bx + C = 0 \) to have real roots, the discriminant \( D \) must be greater than or equal to zero: ...
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