15. If [tex]\alpha[/tex] and [tex]\beta[/tex] are the zeroes of the polynomial [tex]p(x) = k x^2 - 30 x + 45 k[/tex] and [tex]\alpha + \beta = \alpha \beta[/tex], then the value of [tex]k[/tex] is:

A. [tex]-\frac{2}{3}[/tex]
B. [tex]-\frac{3}{2}[/tex]
C. [tex]\frac{3}{2}[/tex]
D. [tex]\frac{2}{3}[/tex]



Answer :

Given the polynomial [tex]\( p(x) = kx^2 - 30x + 45k \)[/tex], we need to find the value of [tex]\( k \)[/tex] such that the zeroes [tex]\( \alpha \)[/tex] and [tex]\( \beta \)[/tex] of the polynomial satisfy [tex]\( \alpha + \beta = \alpha \beta \)[/tex].

Step 1: Identify the coefficients
The polynomial is in the form [tex]\( ax^2 + bx + c \)[/tex], where:
- [tex]\( a = k \)[/tex]
- [tex]\( b = -30 \)[/tex]
- [tex]\( c = 45k \)[/tex]

Step 2: Use properties of polynomial zeroes
For a quadratic polynomial [tex]\( ax^2 + bx + c \)[/tex], the sum and product of zeroes are given by:
- Sum of zeroes [tex]\( \alpha + \beta = -\frac{b}{a} \)[/tex]
- Product of zeroes [tex]\( \alpha \beta = \frac{c}{a} \)[/tex]

Step 3: Calculate the sum and product of zeroes
- Using the formula for the sum of zeroes:
[tex]\[ \alpha + \beta = -\frac{b}{a} = -\left(\frac{-30}{k}\right) = \frac{30}{k} \][/tex]
- Using the formula for the product of zeroes:
[tex]\[ \alpha \beta = \frac{c}{a} = \frac{45k}{k} = 45 \][/tex]

Step 4: Apply the given condition
We know from the problem statement that [tex]\( \alpha + \beta = \alpha \beta \)[/tex]. Therefore:
[tex]\[ \frac{30}{k} = 45 \][/tex]

Step 5: Solve for [tex]\( k \)[/tex]
To find [tex]\( k \)[/tex]:
[tex]\[ \frac{30}{k} = 45 \implies 30 = 45k \implies k = \frac{30}{45} = \frac{2}{3} \][/tex]

Conclusion
The value of [tex]\( k \)[/tex] is:
[tex]\[ \boxed{\frac{2}{3}} \][/tex]