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The value of f’(x) is -1 at the point P on a continuous curve y = f(x). What is the angle which the tangent to the curve at P makes with the positive direction of x axis?(a) π/2(b) π/4(c) 3π/4(d) 3π/2This question was posed to me at a job interview.Asked question is from Application of Derivative topic in chapter Application of Derivatives of Mathematics – Class 12

Answer»

The correct answer is (c) 3π/4

Explanation: Let, Φ be the angle which the TANGENT to the curve y = f(X) at P makes with the positive direction of the x axis.

Then,

tanΦ = [f’(x)]p = -1

= -TAN(π/4)

So, it is CLEAR that this can be written as,

= tan(π – π/4)

= tan(3π/4)

So, Φ = 3π/4

Therefore, the required angle which the tangent at P to the curve y = f(x) makes with positive direction of x axis is 3π/4.



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