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The parabolas y=x2+1y=x^2+1 and y=19(xa)2y=19-(x-a)^2 are tangent to one another and tangent to the line y=mx+by=mx+b. Find mm and bb.

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Q. The parabolas y=x2+1y=x^2+1 and y=19(xa)2y=19-(x-a)^2 are tangent to one another and tangent to the line y=mx+by=mx+b. Find mm and bb.
  1. Find Derivatives: We know that if two curves are tangent to each other at a point, they have the same slope at that point. The slope of a curve given by y=f(x)y=f(x) is the derivative f(x)f'(x). Let's find the derivatives of the given parabolas.\newlineFirst parabola: y=x2+1y = x^2 + 1\newlineDerivative: dydx=2x\frac{dy}{dx} = 2x\newlineSecond parabola: y=19(xa)2y = 19 - (x - a)^2\newlineDerivative: dydx=2(xa)\frac{dy}{dx} = -2(x - a)
  2. Set Equal Slopes: Since the parabolas are tangent to each other, their slopes are equal at the point of tangency. Therefore, we can set their derivatives equal to each other to find the xx-coordinate of the point of tangency.\newline2x=2(xa)2x = -2(x - a)\newlineSolving for xx gives us:\newline2x=2x+2a2x = -2x + 2a\newline4x=2a4x = 2a\newlinex=a2x = \frac{a}{2}
  3. Calculate Tangency Point: Now we need to find the yy-coordinate of the point of tangency by substituting x=a2x = \frac{a}{2} into either of the original equations. We'll use the first parabola's equation.y=(a2)2+1y = \left(\frac{a}{2}\right)^2 + 1y=a24+1y = \frac{a^2}{4} + 1
  4. Determine Line Equation: The line y=mx+by=mx+b is tangent to both parabolas, which means it has the same slope as the parabolas at the point of tangency. Therefore, mm must be equal to the derivative of the parabolas at the point of tangency.\newlinem=2x=2(a/2)=am = 2x = 2(a/2) = a
  5. Find Value of a: To find bb, we need to use the point of tangency (a2,a24+1)(\frac{a}{2}, \frac{a^2}{4} + 1) and the slope m=am=a in the equation of the line y=mx+by=mx+b.\newlinea24+1=a(a2)+b\frac{a^2}{4} + 1 = a(\frac{a}{2}) + b\newlineSolving for bb gives us:\newlineb=a24+1a24b = \frac{a^2}{4} + 1 - \frac{a^2}{4}\newlineb=1b = 1
  6. Solve Quadratic Equation: We have found that m=am = a and b=1b = 1. However, we still need to determine the value of aa. To do this, we need to use the fact that the second parabola is also tangent to the line y=mx+by=mx+b. We substitute y=mx+by=mx+b into the second parabola's equation and solve for aa.\newline19(xa)2=ax+119 - (x - a)^2 = ax + 1
  7. Calculate Discriminant: Expanding the equation and collecting like terms gives us:\newline19x2+2axa2=ax+119 - x^2 + 2ax - a^2 = ax + 1\newlinex2+(2aa)x+(19a21)=0-x^2 + (2a - a)x + (19 - a^2 - 1) = 0\newlinex2+ax+(18a2)=0-x^2 + ax + (18 - a^2) = 0
  8. Solve for aa: Since the line is tangent to the parabola, this quadratic equation must have exactly one solution for xx. This means the discriminant of the quadratic equation must be zero.\newlineDiscriminant: (a)24(1)(18a2)=0(a)^2 - 4(-1)(18 - a^2) = 0\newlinea2+4(18a2)=0a^2 + 4(18 - a^2) = 0\newlinea2+724a2=0a^2 + 72 - 4a^2 = 0\newline3a2+72=0-3a^2 + 72 = 0
  9. Determine Possible Slopes: Solving for aa gives us:\newline3a2=72-3a^2 = -72\newlinea2=24a^2 = 24\newlinea=±24a = \pm\sqrt{24}\newlinea=±26a = \pm2\sqrt{6}\newlineSince m=am = a, we have two possible values for mm: m=26m = 2\sqrt{6} or m=26m = -2\sqrt{6}.
  10. Determine Possible Slopes: Solving for aa gives us:\newline3a2=72-3a^2 = -72\newlinea2=24a^2 = 24\newlinea=±24a = \pm\sqrt{24}\newlinea=±26a = \pm2\sqrt{6}\newlineSince m=am = a, we have two possible values for mm: m=26m = 2\sqrt{6} or m=26m = -2\sqrt{6}.We have two possible slopes for the line, m=26m = 2\sqrt{6} or m=26m = -2\sqrt{6}, and the y-intercept b=1b = 1. These are the values of mm and bb for the line tangent to both parabolas.

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