For what values of a and b is the line -2x + y = b tangent to the curve y=ax^3 when x=5? No decimal answers.
Hello,
\(y=2x+b \\\\
y=ax^3\\\\
slope\ =\ 3ax^2\\
if \ x=5\ then\ slope=75a\ =2\\\\
a= \dfrac{2}{75}\ and \ y= \dfrac{2}{75}* x^3\\\\
if \ x=5\ then\ y=\dfrac{2}{75}* 5^3= \dfrac{10}{3} \\\\
\dfrac{10}{3}=2*5+b\\\\
b= \dfrac{-20}{3}\)
the tangent of the curve is determined by getting the first derivative of teh equation of the curve and substituting with the given data. in this case, the derivative of y=ax^3 is y' = 3a x^2. when x is equal to 5, y' = 3a (25) = 75 a
x=5; y = 125 a
y-y1 = m(x-x1)
y-125 a = 75 a (x-5)
y = 75 ax -500
-2x + y = b
-2(75/2) x + y = -500
a = 75/2
b = -500