Question

For which value of c is the line y=3x+c a tangent to the parabola with equation y=x2-5x+7

Answer 1

Hello :
the slope of tangent in A(x':y') is : f'(x') =3
f'(x) = 2x-5
2x'-3 =3
2x' = 6
x' = 3
f(3)= 3²-5(3)+7=1
1 =3(3)+c
c =-8