Q. Find the value of k such that 3x2+2kx−k−5 has the sum of the zeroes as half of their product.
Denote the zeroes: Let's denote the zeroes of the polynomial by α (alpha) and β (beta). According to Vieta's formulas, for a quadratic polynomial ax2+bx+c, the sum of the roots is −ab and the product of the roots is ac. In our case, the polynomial is 3x2+2kx−(k+5), so a=3, b=2k, and c=−(k+5).
Find sum of roots: First, we find the sum of the roots using Vieta's formula: α+β=−ab=−32k.
Find product of roots: Next, we find the product of the roots using Vieta's formula: αβ=ac=−3(k+5).
Use given relation: The problem states that the sum of the zeroes is half of their product. This gives us the equation: α+β=21×αβ. Substituting the expressions we found for the sum and product of the roots, we get: −32k=21×(−3k+5).
Solve for k: Now, we solve for k. Multiplying both sides by 3 to eliminate the denominator, we get: −2k=21×−(k+5). Then, multiplying both sides by 2 to get rid of the fraction, we have: −4k=−(k+5).
Final value of k: Simplifying the equation, we add k to both sides to get: −3k=−5. Then, we divide both sides by −3 to solve for k: k=−3−5.
Final value of k: Simplifying the equation, we add k to both sides to get: −3k=−5. Then, we divide both sides by −3 to solve for k: k=−5/−3.Finally, we simplify the fraction to get the value of k: k=5/3.