by Morman on August 19th, 2008

Morman

Question

Help answer this question below.

Anyone know how to explain why the formula d/dx (inverse sine x) equals 1/[(1-x^2)^0.5]

Answers. 1 helpful answer below.

  • by bobbinhood on August 22nd, 2008

    bobbinhood

    First, set y between -pi/2 and pi/2. That is, -pi/2 is less than or equal to y, which is less than or equal to pi/2.

    Let y=arcsin(x)
    Then sin(y)=x

    Now differentiate implicitly with respect to x.
    cos(y)y'=1
    y'=1/[cos(y)]

    Because y must be between -pi/2 and pi/2, cos(y) must be nonnegative (greater than or equal to zero).
    Therefore, cos(y) may be written as:
    square root[1-sin^2(y)]
    Substituting x back in for sin(y), we get
    cos(y)=square root[1-x^2]

    Using this substitution for cos(y), we get:
    y'=1/cos(y)
    y'=1/[square root(1-x^2)] provided x is between -1 and 1.

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