# How do I show that both sides of these trigonometric identities are equal to each other?

##
1.) #sintheta = costhetatantheta#

2.) #sin^2theta-cos^2theta=1-2cos^2theta#

1.)

2.)

##### 1 Answer

May 15, 2018

See explanation

#### Explanation:

...pretty straightforward, I think:

First one:

...remember that

so:

...and the

What you have to do for the second one is add

to both sides:

...the above is a trig identity you should know by heart, so this shows that the original formula is a valid identity.

GOOD LUCK