Is 1/sec 20° Equivalent to Cosine in Sin² 20° + 1/sec² 20° = 1?

[CrossFit415]

Homework Statement

Sin^{2} 20\circ + 1/sec^{2} 20\circ = 1 ?

Because isn't 1/sec the same as cosin?

Homework Equations

The Attempt at a Solution

 

[Mark44]

Homework Statement

Sin^{2} 20\circ + 1/sec^{2} 20\circ = 1 ?

Because isn't 1/sec the same as cosin?

Yes. The above identity is true not only for 20 deg., but also for any angle x for which sec(x) is defined.

 

[CrossFit415]

Thanks