Equation of a straight line which is tangent to a curve

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For the curve f(x) = x - 1/3x^2 (one third x squared), find the equation of the straight line which is tangent to this curve at the point x = 1.

Equation of the curve= f(x) = x - 1/3x^2
y= x- 1/3 x ^2
Finding derivative is easy
Derivative of x ^n is n x ^ (n-1)
Thus derivative of x ^2 is
2 x ^(2-1)= 2 x ^ 1 that is 2x
Derivative of x is
x= x ^1
therefore ...