Q. For which values of b will bx+x2+35 have a minimum value of 19 ? If there is more than one answer, separate them using a comma.
Quadratic Function Form: The given function is a quadratic function of the form f(x)=ax2+bx+c. To find the minimum value of a quadratic function, we can use the vertex form of a parabola, which is given by f(x)=a(x−h)2+k, where (h,k) is the vertex of the parabola. The minimum value of the function is k when a>0.
Comparison with Standard Form: The given function is f(x)=x2+bx+35. We can compare this with the standard form of a quadratic function, which is f(x)=ax2+bx+c. Here, a=1, b is the coefficient we need to find, and c=35.
Vertex Calculation: The vertex of the parabola represented by the quadratic function is given by the formula h=−2ab. Since a=1, we have h=−2b.
Minimum Value Determination: The minimum value of the function occurs at the vertex. The y-coordinate of the vertex, k, is the minimum value of the function. We are given that the minimum value is 19, so k=19.
Substitution and Equation Setup: To find the minimum value k, we substitute x=h into the function f(x)=x2+bx+35 and set it equal to 19. This gives us the equation (h)2+b(h)+35=19.
Solving for b: Substituting h=−2b into the equation, we get (−2b)2+b(−2b)+35=19. Simplifying this, we get 4b2−2b2+35=19.
Final Steps: Simplifying further, we combine like terms to get (b2/4)−(2b2/4)+35=19, which simplifies to (−b2/4)+35=19.
Conclusion: Subtracting 35 from both sides of the equation, we get (−b2/4)=19−35, which simplifies to (−b2/4)=−16.
Final Answer: Multiplying both sides of the equation by −4 to solve for b2, we get b2=64.
Final Answer: Multiplying both sides of the equation by −4 to solve for b2, we get b2=64. Taking the square root of both sides of the equation, we find that b can be either 8 or −8, since both numbers squared give 64.