How do you prove sec^2(csc^2) = sec^2 + csc^2?

2 Answers
May 4, 2016

see below

Explanation:

Right Side: =sec^2x+csc^2x

=1/cos^2x + 1/sin^2 x

=(sin^2x+cos^2x)/(cos^2xsin^2x)

=1/(cos^2xsin^2x)

=1/cos^2x * 1/sin^2x

=sec^2xcsc^2x

= Left Side

May 4, 2016

Note the following identity:

csc^2theta = 1 + cot^2theta

So, let's see how that works out.

\mathbf(sec^2theta(csc^2theta) = sec^2theta + csc^2theta)

sec^2theta(1 + cot^2theta) = sec^2theta + csc^2theta

sec^2theta + sec^2thetacot^2theta = sec^2theta + csc^2theta

Lastly, use the identities

  • cot^2theta = cos^2theta/sin^2theta,
  • 1/sin^2theta = csc^2theta,
  • 1/cos^2theta = sec^2theta,

to get:

sec^2theta + sec^2theta(cos^2theta/sin^2theta) = sec^2theta + csc^2theta

sec^2theta + 1/cancel(cos^2theta)(cancel(cos^2theta)/sin^2theta) = sec^2theta + csc^2theta

sec^2theta + 1/sin^2theta = sec^2theta + csc^2theta

color(blue)(sec^2theta + csc^2theta = sec^2theta + csc^2theta)